Title of Invention: Adjustable Bedding Height and Lengthwise Positioning Apparatus Description Cross-Reference to Related Applications and Claim of Priority The present application is related to and claims the benefit of U.S. Non-Provisional Patent Application No.16/577,263 filed September 20, 2019 entitled “Adjustable Bedding Cover Height and Lengthwise Positioning Apparatus” and U.S. Non-Provisional Patent Application No.17/022,502 filed September 16, 2020 entitled “Adjustable Bedding Cover Height and Lengthwise Positioning Apparatus,” each of which are hereby incorporated by reference into the present application as if fully set forth herein. Technical Field This invention relates to selectively adjusting bedding away from a person’s feet while also facilitating changing the lengthwise positioning of the bedding covers. Background Art For comfort and warmth, a person generally wishes to have one or more of a sheet, a blanket, a bedspread, or a comforter (individually, and collectively, “bedding”) covering the person’s body. Generally, the bedding is tucked in at the foot of the bed between the frame or box spring and the mattress. Because sheets are a standard length, the more sheet that is tucked in, and the thicker the mattress, the less sheet is available to cover the individual. Thus, individuals sleeping on their backs, taller individuals, and/or individuals sleeping on thicker mattresses (certain mattresses are 18” thick) may feel that the sheet or bedding is “too short”, that is, it does not extend far enough on the top part of the individual’s body to provide the desired comfort and warmth. Further, when a person is sleeping on his/her back, his/her feet generally point upward, rather than lying flat against the mattress. The weight of the bedding on the person’s feet, exaggerated by the tension caused by the bedding being tucked in at the foot of the bed, tends to force the feet toward a downward pointing position, which many people find uncomfortable. Further, persons with foot or ankle injuries, or irritated skin, such as from sunburn, poison ivy, burns, or other conditions, often find any contact, weight, or pressure by the bedding on their feet to be uncomfortable or even painful. An adjustable bedding cover height and lengthwise positioning apparatus, described below, positions the bedding away from the person’s feet, thereby assisting the person in getting a good night’s sleep, while also facilitating changing the lengthwise positioning of the bedding covers. Moreover, many attempts have been made to create devices that introduce fresh air circulation into the area between bedcovers and a sleeping person. Experts calculate that the average adult delivers 17 gallons per year of perspiration into this environment and that if people can sleep cooler, they sleep better. Various fans and ducted fan combinations are on the market to address this problem and each solution suffers varying degrees of high cost, bulkiness, aesthetic displeasure and generally inadequate air exchange performance. Introducing low pressure air quietly into an area devoid of open compartments or chambers is a losing proposition. If available, an open chamber within the bedcover environment would alleviate the resistance to air introduction and create a microclimate opportunity for air exchange, temperature control and humidity control. Disclosure of Invention In accordance with one form of this invention, there is provided an adjustable bedding cover height and lengthwise positioning apparatus having a base configured for positioning between a bed frame and a mattress; at least one riser; a connection section connected between the base and the at least one riser; and a clip connected to the at least one riser to secure the bedding to the apparatus, the clip being movable along at least a portion of the at least one riser. In accordance with another form of this invention, there is provided an adjustable bedding cover height and lengthwise positioning apparatus having an integral base and riser unit, the base being configured for positioning between a bed frame and an adjacent mattress; and a moveable clip connected to the riser of the integral base and riser unit to secure bedding to the apparatus, the clip being moveable along at least a portion of the riser of the integral base and riser unit. Brief Description of the Drawings The subject matter which is regarded as the invention is set forth in the appended claims. The invention itself together with further objects and advantages may be better understood in reference to the following description taken in conjunction with the accompanying drawings in which: Figure 1 is an illustration of a bed having a frame and a mattress, with an adjustable bedding cover height and lengthwise positioning apparatus lying on top of the bed; Figure 2 is an illustration of a bed showing the bedding and also showing the apparatus in a collapsed position and placed between the frame and the mattress; Figure 3 is an illustration of a bed showing the apparatus in an extended position and elevating the bedding at the foot of the bed; Figure 4 illustrates one implementation of the apparatus having a base, a connecting section, first and second telescoping interior risers, first and second telescoping exterior risers, a top support, a plurality of locking holes in the telescoping exterior risers, depressible locking pins, and a clip; Figure 5 is an exploded view showing the base, the back side of the base, the connecting section, and the telescoping risers; Figure 6 illustrates a rear perspective view of the apparatus; Figure 7 illustrates a rear perspective view of the apparatus with the telescoping risers in an extended position so as to raise the height of the bedding in order to adjust to the height of the mattress; Figure 8 is an illustration wherein there are four sets of telescoping risers. Figure 9 illustrates the apparatus in a folded position; Figure 10 illustrates the apparatus in a folded position and also illustrates details of construction of the clip; Figure 11 illustrates the apparatus in a folded position, illustrates details of construction of the clip and illustrates the apparatus with the clip in a depressed position; Figure 12 illustrates an implementation wherein the top support is not used; Figure 13 illustrates the implementation of FIG.12 where the telescoping risers are collapsed, and the clip is positioned at the lower end of the risers; Figure 14 illustrates the implementation of FIG.13 wherein the apparatus is folded, such as for bedding makeup and stowage; Figure 15 illustrates an environment of the apparatus of FIG.4 wherein a heating pad or blanket is draped over the apparatus to provide additional heating or warmth for the feet of the user; Figure 16 illustrates the apparatus adjusted to different heights to accommodate a user preference with respect to the height of the mattress; Figure 17 illustrates another embodiment of the apparatus; Figure 18 illustrates a side view of the apparatus of Fig.17; Figure 19 illustrates the apparatus of FIG.17 in a folded position; Figure 20 illustrates a front elevational view of another embodiment of the apparatus wherein the top support is expandable; Figure 21 illustrates the implementation of FIG.20 wherein the top support of the apparatus is expanded; Figure 22 illustrates another embodiment of the apparatus having a base, a single riser having a slot therein, and a clip; Figure 23 illustrates the implementation of FIG.22 wherein the single riser is in a raised position; Figure 24 illustrates a side view of a construction of the clip for use in the apparatus of FIGs.22 and 23; Figure 25 illustrates another embodiment of the apparatus having a base, a single riser having a slot therein, a clip, and a “T”-shaped top support; Figure 26 illustrates the implementation of FIG.25 wherein the single riser is in a raised position; Figure 27 illustrates another embodiment of the apparatus having a fan; Figure 28 illustrates an isolated view of the implementation of FIG.27 shown in partial cross-section illustrating the fan for use in the apparatus; and Figure 29 is an illustration of a bed showing the bedding and also showing the apparatus of the implementation of FIGs.27 and 28 illustrating operation of the fan. Best Mode(s) for Carrying Out the Invention An adjustable bedding cover height and lengthwise positioning apparatus is disclosed herein. Prior to discussion of the construction of the adjustable bedding cover height and lengthwise positioning apparatus it may be beneficial to discuss a typical environment in which the apparatus might be used. FIG.1 is an illustration of a bed 10 having a frame 12 and a mattress 14, with the adjustable bedding cover height and lengthwise positioning apparatus 30 (hereinafter the “apparatus”) lying on top of the bed 10. An optional headboard 16 is also shown. Some beds are made with a frame, other beds are made with a box spring, depending upon customer and manufacturer preferences. Therefore, to avoid having to repeatedly express these components in the alternative, such as “frame or box spring,” the term “frame,” as used herein, also includes a box spring. For convenience of illustration, the bedding reference numeral 18 in FIG.2) is not shown but would be placed on the bed 10 and a portion of the foot of the bedding would be clipped into the apparatus 30. FIG.2 is an illustration of a bed 10 showing the bedding 18 and also showing the apparatus 30 in a collapsed position and placed between the frame 12 and the mattress 14. The bedding 18 is still clipped to the apparatus 30 so, as the apparatus 30 is tucked between the frame 12 and the mattress 14, the bedding 18 is also tucked between the frame 12 and the mattress 14. Bedding 18 may, for example, include one or more top sheets, one or more blankets, a bedspread, cover, quilt, and/or comforter. Although not shown for convenience of illustration, the bed 10 may optionally also have one or more pillows, a footboard, a mattress pad, and/or a bottom sheet (often a fitted sheet). FIG.3 is an illustration of a bed 10 showing the apparatus 30 in an extended position and elevating the bedding 18 at the foot 11 of the bed 10. FIG.4 illustrates one implementation of the apparatus 30 having a base 32, a connecting section 34 (34A, 34B, 34C), first and second telescoping interior risers 36A, 36B, first and second telescoping exterior risers 38A, 38B, top support 40, a plurality of locking holes 42 in the telescoping exterior risers 38A, 38B, depressible locking pins 44, and a clip 46. The telescoping risers 36A, 36B, 38A, 38B may be considered to be extendable risers. The base 32 preferably has at least two legs 32A, 32C and a back side 32B. More preferably, the base 32 also has a front side 32D for additional rigidity. The connecting section 34 has a center section 34A, a right arm 34B, and a left arm 34C. Preferably, the apparatus 30 has a width between the telescoping risers 36A, 36B, 38A, 38B which is approximately the same as the width between the user’s feet when the user is sleeping on his or her back in the bed 10. In an embodiment, the top support 40 is in the form of an arch. Also, in an embodiment, the base 32 preferably has one or more friction strips 39 (39A, 39B, 39C) attached thereto, such as by glue, double-sided tape, or another convenient adhesive. The strips 39 are made of a non-slippery material, such as rubber, so as to prevent the apparatus 30 from slipping around once it is inserted between the frame 12 and the mattress 14. Although the strips 39 are shown on the top side of the base 32, the strips 39 could also be placed on the bottom side of the base 32, or on both sides of the base 32. Also, the strips 39A, 39B, 39C could be a single continuous strip, or two strips, or four or more strips, as desired, rather than being three strips. The shape, length, width, and positioning of the strip or strips 39, as shown, is exemplary and may be varied. FIG.5 is an exploded view showing the base 32, the back side 32B of the base 32, the connecting section 34 (34A, 34B, 34C), and the telescoping risers 36A, 36B. FIG.6 illustrates a rear perspective view of the apparatus 30. The back side 32B of the base 32 is configured to accept the center section 34A. The back side 32B of the base 32 may be configured, for example, as an elongate inverted “U” into which the center section 34A is inserted. This allows rotation of the base 32 with respect to the other components 34, 36, 38, and 40, so that the apparatus 30 may be folded over to place components 34.36. 38, and 40 in a position substantially parallel to the base 32. In use, the base 32 is placed between the frame 12 and the mattress 14. Returning to FIGs.4 and 5, an upper portion of the right arm 34B and an upper portion of the left arm 34C are at least partially inserted into, and are preferably movable within, lower telescoping risers 36A and 36B, respectively, by, for example, press fit, friction fit, adhesive, or screws. In another embodiment, the upper portions of the right arm and left arm 34B and 34C are fixed within the lower telescoping risers 36A and 36B, respectively, by, for example, welding. In another embodiment, there is a mechanical stop on the upper portions of the right riser and left riser 34B and 34C and/or the lower telescoping risers 36A and 36B, to prevent inadvertent separation thereof. The lower telescoping risers 36A, 36B, are at least partially inserted into the upper telescoping risers 38A and 38B, respectively, and may be moved further into, or out of, the upper telescoping risers 38A, 38B so as to adjust the height of the apparatus 30. The upper telescoping risers 38A, 38B have a plurality of locking holes 42, and each lower telescoping riser 36A, 36B has a depressible locking pin 44. A locking pin 44 protrudes though a locking hole 42 to fix the risers 36, 38 with respect to each other so as to provide a desired fixed height of the bedding 18 above the mattress 14. When locking pin 44 is depressed, the risers 36, 38 are slidable relative to each other to adjust the height. By adjusting the risers 36, 38, the user can adjust the height of the top support 40 above the mattress 12. The top support 40 is beneath the bedding 18. Therefore, adjusting the risers 36, 38 adjusts the height of the top support 40, which adjusts the height of the bedding 18 above the mattress 14. The risers 36, 38 are preferably adjusted to provide a height for the top support 40 which prevents the bedding 18 from contacting or weighing on the user’s feet. The height of the bedding 18 is preferably not raised so much that outside air is allowed to come under the bedding 18. It will be appreciated that when the apparatus 30 is extended then the bedding 18 may be disposed to slip over the top support 40 and then fall onto the user’s feet. The clip 46 (FIGs.4, 6) captures the bedding 18 to prevent such slipping. Preferably, the clip 46 is fixed to the telescoping interior risers 36A, 36B toward the bottom of those risers. The bedding 18 is captured between the clip 46 and the risers 38. In another implementation, the clip 46 may be adjustable along the length of the telescoping interior risers 36A, 36B. The clip 46 may then be used, for example, in a raised position (not shown), away from the bottom of risers 36A, 36B, such as when the mattress 14 has a thickness that requires a raised position of the clip in order to maintain proper bedding length. In another implementation, the clip 46 may also be adjustable along the length of the telescoping exterior risers 38A, 38B. The clip 46 may then capture the bedding 18 between the clip 46 and the risers 38 or, if desired, between the clip 46 and the top support 40. If the clip 46 is adjustable, then it may be held in a desired position by any user- convenient means, such as, for example, by friction, screws, protrusions which mate with the holes 46, etc. FIG.7 illustrates a rear perspective view of the apparatus 30 with the telescoping risers 36A, 36B, 38A, 38B in an extended position so as to raise the height of the bedding 18 in order to accommodate the height of the mattress 14. In another implementation, there may be more than two sets telescoping risers. FIG. 8 is an illustration wherein there are four sets of telescoping risers: (1) 36A and 36B, (2) 37A1 and 37B1, (3) 37A2 and 37B2, and (4) 38A and 38B. There may also be only three sets of telescoping risers, such as by omitting set 37A2 and 37B2. The clip 46 may be fixedly attached to a set of risers or may be adjustable to be positioned on any set of risers. Thus, the clip 46 may be adjusted to best retain the bedding 18 in a desired position. FIGs.9 - 11 illustrate the apparatus 30 in a folded position for (1) bedding makeup, wherein a user may use the clip 46 to selectively secure the bedding 18 to the apparatus 30 prior to the user placing the apparatus 30 between the frame 12 and the mattress 14, and (2) stowing the apparatus 30, such as under the bed 10 or between the mattress 14 and the frame 12. FIGs.10 and 11 also illustrate details of construction of the clip 46. The clip 46 preferably comprises a pair of cylindrical retaining components 46A, a bedding retaining component 46B, and a pair of pins 46C. The cylindrical retaining components 46A may either be fixed in position on the telescoping interior risers 36A, 36B, may be adjustable in position thereon, or may also be adjustable in position on the telescoping exterior risers 38A, 38B. Bedding retaining component 46B is preferably in the shape of an arch and is pivotable on pin 46C so that the bedding retaining component 46B can capture and hold the bedding 18 to prevent slippage thereof. Clip 46 also preferably has at least one friction strip 47 attached thereto, such as by glue, double-sided tape, or another convenient adhesive. The friction strip 47 is made of a non-slippery material, such as rubber, so as to prevent the bedding 18 from slipping off of the clip 46. Also, the strip 47 could be two or more strips, as desired, rather than being a single strip. The shape, length, width, and positioning of the strip or strips 47, as shown, is exemplary and may be varied. FIG.11 illustrates the apparatus 30 with the clip 46 in a depressed position whereby the bedding 18 may be captured by the bedding retaining component 46B and, therefore, held by the clip 46, prior to the apparatus 30 being placed between the frame 12 and the mattress 14. FIG.12 illustrates an implementation wherein the top support 40 is not used. Rather, the clip 46 is preferably positioned at the top end of the telescoping exterior risers 38A, 38B, so as to hold the bedding 18 against the telescoping exterior risers 38A, 38B and/or top caps 48A (FIG.13), 48B. FIG.13 illustrates the implementation of FIG.12 where the telescoping risers are collapsed, and the clip 46 is positioned at the lower end of the risers 38A, 38B. FIG.14 illustrates the implementation of FIG.13 wherein the apparatus 30 is folded, such as for bedding makeup and stowage. FIG.15 illustrates an environment of the apparatus of FIG.4 wherein a heating pad or blanket 50 is draped over the apparatus 30 to provide additional heating or warmth for the feet of the user. FIG.16 illustrates the apparatus 30 adjusted to different heights H1, H2, H3 to accommodate a user preference with respect to the height of the mattress 14. FIG.17 illustrates another embodiment of the apparatus 30. In this embodiment there is a base 32, a connecting section 34, a single telescoping interior riser 36, the connecting section 34 is preferably, but not necessarily, rotatably connected to the telescoping interior riser 36 at a joint 60, a single telescoping exterior riser 38, a clip 46, and an optional top support 40. The telescoping risers 36, 38 may be considered to be a single extendable riser. Also shown are a plurality of locking holes 42 in the telescoping exterior riser 38 and a depressible locking pin 44, which allow adjustment of the height of the apparatus 30 by adjusting the position of the telescoping exterior riser 38 along the telescoping interior riser 36. Although only two telescoping risers 36, 38 are shown, there may be three or more telescoping risers, if desired, all forming the extendable riser. In this embodiment, the base 32 and top support 40 are preferably “T”-shaped with the base of the “T” preferably being approximately midway of the cross of the “T”. Also, either or both the base 32 and the top support 40 may be in the shape of an arch. The clip 46 captures the bedding 18 against the telescoping exterior riser 38 to prevent slippage of the bedding 18, as discussed above. Also, the apparatus 30 preferably includes at least one friction strip 39 so as to prevent the apparatus 30 from slipping around once it is inserted between the frame 12 and the mattress 14. FIG.18 illustrates a side view of the apparatus 30 of Fig.17. FIG.19 illustrates the apparatus 30 of FIG.17 in a folded position. FIGs.20 and 21 illustrate another embodiment of the apparatus 30 wherein the top support is expandable. The illustration is a rear view of the apparatus 30 when in the folded position. In this embodiment the top support has a center section 40A, a left arm 40B, and a right arm 40C. The left arm 40B and the right arm 40C are attached to the center section 40A by joints or hinges 40D and 40E. In FIG.20 the arms 40B, 40C are in a folded position, and in FIG.21 the arms 40B, 40C are in a fully expanded position. The arms 40B, 40C may also be placed, if desired, in a position between the folded position and fully expanded position. The arms 40B, 40C may be held in a desired position by, for example, friction, detents, pins, latches, or other convenient mechanism. FIGs.22 and 23 illustrate another embodiment of the apparatus 30, having a base 32, a single riser 38D having a slot 38E therein, and a clip 46. Preferably, but not necessarily, the base 32 and the single riser 32D are a single, unitary construction. In this embodiment the base32 is preferably, but not necessarily, in the shape of a truncated triangle, with the truncated end of the triangle being joined to the riser 38D. Also shown is a friction strip 39. In this embodiment the height between the base 32 and the top of the riser 38D is fixed, but the clip 46 can be adjusted up or down as needed and may be held in the desired position either by friction or a restraining mechanism. FIG.24 illustrates a side view of a construction of the clip 46 for use in the apparatus 30 of FIGs.22 and 23. The clip 46 has a shaft 46D which rides in the slot 38E. At the end of the shaft 46D is a knob, ball, plate, or other retaining device 46E which holds the clip 46 and the riser 38 together. The clip 46 may be placed in any desired position on the riser 38 by sliding the clip 46 up or down on the riser 38. The clip 46 may be held in the desired position by, for example, friction, detents, pins, latches, or other convenient mechanism. The clip 46 holds the bedding 18 against the riser 38D. FIGs.25 and 26 illustrate another embodiment of the apparatus 30 having a base 32, a single riser 38D having a slot 38E therein, a clip 46, and a “T”-shaped top support 40. In FIG.25 the apparatus 30 is shown in the collapsed or lowered position. In FIG.26 the apparatus 30 is shown in the extended or raised position. This embodiment is similar to the embodiment of FIGs.22-24 but, in this embodiment, the lower end of the top support 40 is connected to the clip 46 so that the clip 46 and the top support 40 move up or down the riser 38D as a single unit. This secures the bedding 18 to the bottom of the top support 40 even while the height is being adjusted. Optionally, the top support 40 and the body of clip 46 may be formed as a single unit. FIGs.27 – 29 illustrate another embodiment of the apparatus 30 including a fan 70. In one embodiment, the fan 70 is a cross-flow fan, although other suitable fan types may be also be used. The fan 70 provides active airflow through an inflow channel 72 for ventilating the chamber created when the height of the bedding 18 is adjusted above the mattress 14. When the apparatus 30 is in the extended position, the endmost edge of the bedding 18 is held in position near the upper surface of the mattress edge. This juxtaposition achieves proximate access to room air immediately adjacent to the resultant bedcover chamber, enabling simple and compact active ventilation. Placement of the fan 70 in this area eliminates the shortcomings of previous devices intended for introduction of fresh air under the bedding 18. Through a short distance, room air can be drawn into the open chamber created by the bedding 18 by the fan 70 and then exhausted out openings adjacent to both the inflow channel 72 and the user. It will now be appreciated that one implementation of an adjustable bedding cover height and lengthwise positioning apparatus has: a base configured for positioning between a bed frame and a mattress; at least one riser; a connecting section connected between the base and the at least one riser, the connecting section being optionally rotatably connected to the base to allow rotation of the at least one riser with respect to the base; and a movable clip connected to the at least one riser to secure the bedding to the apparatus, the clip being movable along at least a portion of the at least one riser. Another implementation of the adjustable bedding cover height and lengthwise positioning apparatus has a top support connected to the movable clip. In another implementation of the adjustable bedding cover height and lengthwise positioning apparatus the at least one riser has a slot running lengthwise through at least a portion of the at least one riser, and the movable clip has a shaft which extends through the slot. It will now be appreciated that another implementation of an adjustable bedding cover height and lengthwise positioning apparatus has: a base having a first leg and an opposing second leg, the first and second legs configured to allow positioning of the base and a least a portion of the first leg and at least a portion of the second leg between a bed frame and an adjacent mattress; a first extendable riser and an opposing second extendable riser; a connecting section, connected to the first and second extendable risers and, optionally, rotatably connected to the base to allow rotation of the first and second extendable risers with respect to the base; a clip connected to and between the first and second extendable risers. Another implementation of an adjustable bedding cover height and length apparatus has: a base having a first leg and an opposing second leg, the first and second legs configured to allow positioning of a least a portion of the first leg and at least a portion of the second leg between a bed frame and an adjacent mattress; a first extendable riser and an opposing second extendable riser; a connecting section, connected to the first and second extendable risers and, optionally, rotatably connected to the base, to allow rotation of the first and second extendable risers with respect to the base; and a top support connected to and between the first and second extendable risers toward or at the top of the first and second extendable risers. The adjustable bedding cover height and length apparatus may have both the clip and the top support. The first and second extendable risers may each be two or more telescoping tubes. The clip may be movable along the first and second extendable risers. The top support may be an arch. It will also be appreciated that another implementation of an adjustable bedding cover height and lengthwise positioning apparatus has: a base having a leg, the base and leg being configured to allow positioning of the base and a least a portion of the leg between a bed frame and an adjacent mattress; an extendable riser, optionally rotatably connected to the leg to allow rotation of the riser with respect to the base; a clip connected to and between the first and second extendable risers; and a top support connected to the top end of the extendable riser. The base, the support, or both, of the adjustable bedding cover height and length apparatus may be “T”-shaped. The base, the support, or both, of the adjustable bedding cover height and length apparatus may be “T”-shaped where the cross of the “T” is in the shape of an arch. The extendable riser may be two or more telescoping tubes. Referring to the foregoing description of the preferred embodiments of the invention, it would be apparent that many modifications may be made therein. It is to be understood that all such modifications are embodied in the accompanying claims which come within the true spirit and scope of the invention. Industrial Applicability The way in which the invention is capable of being exploited and the way in which it can be made and used will be apparent from the foregoing, particularly in regard to facilitating selective adjustment of bedding away from a person’s feet and changing the lengthwise positioning of the bedding covers.