CLOSURE DEVICE FOR CONTAINERS FIELD OF THE INVENTION The present invention generally relates to devices use for sealing containers that dispense materials. More particularly, the present invention relates to a device that is attachable to a container in order to be actuated by a digit of the hand thus causing the container opening to be exposed and which reseals the container when the device is released. More specifically, the invention is directed to a device for use with drinking containers in order to dispense fluid contents when open but to prevent spillage of the fluid contents when not actuated. BACKGROUND OF THE INVENTION Containers for storing and dispensing materials are found in virtually every aspect of life. Typically, these containers have caps or lids which seal over a mouth portion of the container so as to allow access to the contents. Typically, these caps or lids either attach to the container by screw threads or by a snap-fit engagement. Often, such caps or lids require the user to use both hands to remove the cap or lid to allow access to the contents. Removal, of course, presents a problem should the detachable cap become lost. One common type of container is the plastic drinking bottle that is used for storing and transporting beverages. Such plastic drinking bottles are either disposable or reusable. In either case, however, such drinking bottles typically have a screw-on cap that is detachable when the person decides to drink from the bottle. Although this does not present a problem in many instances, there are circumstances where the removal of the cap presents certain problems. For example, if the user is driving a motor vehicle, riding a bicycle or engaged in other activities a cap that requires the use of both hands presents an inconvenient or dangerous situation; here, the screw-on cap is very inconvenient. Therefore, numerous closure caps have been developed for beverage containers to facilitate the ease of delivery of a container's contents without spillage but which can be open and closed with a single hand. For example, sports bottles have been developed which are provided, by way of example, with one-way valves, positive closure valves and devices which act as a seal and closure valve. Often, such bottles are provided with either a flexible plastic drinking straw the extends from the outside through a hole in the top or with a popup type drinking spout located centrally of the container top. Examples of such container closure mechanisms include those disclosed in U.S. Patent No. 5,607,073, U.S. Patent No. 5,651 ,471 , U.S. Patent No. 5,669,427 and U.S. Patent No. 5,788,125. Pop-up spouts for sports bottles may be effective in allowing access to liquid contents, they nonetheless present certain disadvantages during use. For example, in order to open a pop-up spout, a user will need to use either two hands or, in some instances, users pull the spout open by gripping one hand around the bottle and using his/her teeth to pull on the spout. Oftentimes it is impossible for the user to use both hands, especially during rigorous activity such as bicycle riding and the like. On the other hand, when the user uses one hand and pulls the spout with his/her teeth, there is always the danger of physical damage to the teeth or mouth of the user. In addition, such pop-up spouts usually provide restricted fluid flow due to the relative small sizes of the orifices and seals incorporated in the pop-up spouts. Often a user may want to drink a larger quantity of fluid over a shorter time, which is impossible with such structures. Moreover, many such spouted caps are specifically designed for a particular bottle structure so that the caps may not mount on a variety of different containers. Accordingly, there remains a need for improved end closure devices for containers, especially for drinking bottles. There is a need for such a cap structure which may mount on a variety of different containers and which may readily move between an open and closed position to especially allow access to and enclose the contents of the bottle. There is also a need for such a structure that can allow freer dispensing of liquid contents from the bottle while at the same time being able to be manipulated by one hand of the user without the need to use a second hand or his/her teeth. The present invention is directed to meeting these needs. SUMMARY OF THE INVENTION It is an object of the present invention to provide a new and useful closure device adapted to attach to a container in order to control the dispensing of the contents of the container. It is another object of the present invention to provide a closure device which can easily be operated with one hand of the user. A further object of the present invention is to provide a closure device for a drinking bottle that is biased into a closed position but which can readily be manipulated with a single digit of the hand into an open condition allowing the dispensing of the contents of the bottle. Still a further object of the present invention is to provide a closure device which can secure onto a variety of different drinking bottles or containers. According to the present invention, then, a closure device is provided that is adapted to attach to a container that holds contents, such as a liquid beverage, wherein the container includes a mouth portion that has a surrounding rim providing a mouth through which the contents may be dispensed and wherein the mouth portion includes at least one external lid. Broadly, the closure device includes a mounting member that includes at least one retaining element adapted to engage the external rib thereby to secure the mounting member to the mouth portion of the container to define a mounted state. The mounting member has an opening therethrough that is located to register with the mouth of the container when in the mounted state whereby the contents in the container may be dispensed. An inner seal is supported by the mounting member in surrounding relationship to the opening and is located so as to substantially seal against the mouth portion when in the mounted state. A cap member is pivotally secured to the mounting member at a cap pivot access. The cap member is pivotally moveable between a closed position to retain the contents in the container and an open position to allow dispensing of the contents. A plug portion is disposed on either the mounting member or on the cap member. An outer seal is provided and is disposed on the other of the mounting member and the cap member. The plug portion is adapted to seat in the outer seal when the cap member is in the closed position thereby to substantially seal relative to the outer seal. An actuator member is also pivotally secured to the mounting member at an actuator pivot axis and engages the cap member. The actuator member is manually pivotal between a first position wherein the cap member is in the closed position and a second position wherein the cap member is in the open position. In the disclosed embodiment, the mounting member is cup-shaped in configuration so as to include a surrounding sidewall and an end wall formed by a lip extending inwardly from the sidewall to form the opening. Here, the plug portion is disposed on the cap member and the inner and outer seal may be formed as a common one piece gasket having an orifice therethrough and a peripheral channel sized and adapted to receive the lip thereby to mount to the gasket on the end wall so that an inner portion of the gasket is located in the interior of the mounting member and an outer portion of the gasket is located exteriorly of the mounting member. This, respectively, provides lhe inner and outer seals. The orifice is then coaxial with the opening. Here, also, the plug portion is frustoconical in shape so it is sized to extend into the orifice to seal the outer portion of the gasket. Here, also, the cap member may have a groove extending around the plug portion with the groove being sized and adapted to nestably receive the outer seal from the cap members in the closed position. The cap member is biased towards the closed position by means of a suitable spring element. In the disclosed embodiment, the actuator arm, itself, is biased toward the first position by a spring element, thereby to bias the cap member toward the closed position. In one embodiment, where the external rib on the mouth portion is defined by a first thread structure, the retaining element is formed by retainer threads sized and adapted to threadably mate with a first thread structure. In another embodiment, wherein the external rib on the mouth portion is defined by an outwardly projecting flange, the retaining element is defined by at least one longitudinally extending post disposed on the mounting member and rotatable between selected angular positions. Here, the post includes at least one fastening nub oriented so as to mechanically engage the flange into a first angular position and to disengage the flange into a second angular position. In the disclosed embodiment, a plurality of longitudinal extending posts are provided on the mounting member at equiangularly disposed locations therearound. Moreover, regardless of the number of posts, this embodiment provides a plurality of fastening nubs oriented so as to mechanically engage the flange in respective first angular positions and to disengage the flange in a second angular position. Each fastening nub is then longitudinally and angularly offset from the other fastening nubs relative to the longitude of the post. The actuator member, as disclosed, includes a lever arm and an actuator arm joined at a vertex portion. The actuator arm then terminates in a free end that slidably engages the cap member. The cap member therefore can include a pair of spaced apart opposed wings each having an elongated slot formed therein. The free end of the actuator arm is then sized and adapted to mount between the wing, and the free end of the actuator arm includes oppositely projecting slide pins each slideably engaging a respective one of the slots. Here, also, the mounting member is disclosed to include a pair of spaced apart opposed webs extending longitudinally thereof. The actuator member is then sized and adapted to mount between the webs. Each web may have a hole formed therein and the vertex portion of the actuator member includes oppositely projecting trunions each sized and adapted to be rotatably received in the respective one of the holes in the webs. Moreover, the webs are disclosed to include oppositely projecting axle pins, and the cap member includes a pair spaced apart opposed wings each having a hole adapted to rotatably receive a respective axle pin. These and other objects of the present invention will become more readily appreciated and understood from a consideration of the following detailed description of the exemplary embodiments of the present invention when taken together with the accompanying drawings, in which: BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of a closure device according to a first exemplary embodiment of the present invention shown attached to a representative container in the form of a bottle adapted to receive a liquid beverage; Figures 2(a), 2(b) and 2(c) are side views in elevation of the closure member of Figure 1 shown, respectively, with the cap member in the closed, intermediate and open positions; Figure 3 is a side view in elevation of the mounting member according to a first exemplary embodiment of the present invention; Figure 4 is an end view in elevation of the mounting member of Figure 3; Figure 5 is a top plan view of the mounting member of Figures 3 and 4; Figure 6 is a cross-sectional view of the mounting member of Figures 3 and 4 taken about lines 6-6 of Figure 4; Figure 7 is a perspective view of the gasket that provides inner and outer seals in the present invention; Figure 8 is a front view in elevation of an attachment post used with the mounting member of Figures 3-5; Figure 9 is a side view in elevation of the attachment post of Figure 8; Figure 10 is an enlarged top plan view of a representative post-mounting bore of the mounting member of Figures 3-5; Figure 11 is a cross-sectional view taken about lines 11-11 of Figure 10; Figure 12 is a cross-section view, similar to Figure 11 , but showing the mounting of an attachment post of Figures 8 and 9 in the post-mounting bore; Figure 13 is a side view in elevation of an actuator member used with the closure device shown in Figures 1 and 2(a)-2(c); Figure 14 is an end view in elevation of the actuator member of Figure 13; Figure 15 is a side view in elevation of a cap member used in the closure device according to the first exemplary embodiment of the present invention; Figure 16 is a top plan view of the cap member of Figure 15; Figure 17 is a cross sectional view of the cap member of Figures 15 and 16 taken about lines 17-17 of Figure 16; Figure 18 is a perspective view of a spring element used to bias the actuator arm and cap member into the closed position; Figure 19 is an enlarged, side view in partial cross-section showing the attachment of the closure device according to the first exemplary embodiment of the present invention, in an intermediate position, attached in a mounted state to a container in the form of a drinking bottle;

Figures 20(a), 20 (b) and 20(c) or top views in partial cross-section showing the rotational movement of the attachment posts in the mounting member relative to a container mouth portion; and Figure 21 is a cross-sectional view, similar to Figure 19, but showing a second attentative embodiment of the present invention. DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS The present invention is directed to a closure device that is adapted to attach to a container, such as a drinking bottle and the like. As is known, such containers include a mouth portion that have a surrounding rim providing a mouth through which the contents, such as a liquid beverage may be dispensed. Typically, such mouth portions are provided with an external rib that can be one or more of a combination of threads to receive a threaded cap or circumferential flanges. However, it should be understood, that while the present invention is described with respect to a beverage bottle, the inventive concepts contained herein may be implied to other types of containers, as well. With reference first to Figures 1 and 19, it may be seen that a closure device 10 is shown attached to a container 12 that is in the form of a bottle that, for example, is adapted to hold a liquid beverage for consumption. Such bottles, of course, are commonly known to package such beverages as water, sports beverages, carbonated beverages and the like. As is illustrated in Figure 1 , but with reference also to Figure 19, it may be seen that closure device 10 mounts onto the mouth portion 13 of container 12 and seals against the surrounding rim 14 of mouth 15. As is shown in Figures 2(a)-2(c), closure device 10 broadly includes mounting member 20 a cap member 90 and an actuator member 70. Moreover, closure device 10 is operative to selectively access the contents of container 12 for dispensing. To this end, cap member 90 may move between a closed position shown in Figure 2(a) and an open position shown in Figure 2(c) through an intermediate position shown in Figure 2(b). It may be further seen, in reference to Figures 2(a) and 2(c) that closure device 10 is structured so that pivotal movement of actuator member 70 about an angle "a" results in a larger pivotal movement about an angle "b" of cap member 90. Thus, for example, pivotal movement of actuator member 70 of approximately fifty-five degrees results in the pivoting of cap 90 about one hundred forty degrees. A more detailed structure of mounting member 20 is illustrated in Figures 3-6. Here, it may be seen that mounting member 20 includes a surrounding sidewall 22 and an end wall 24 with end wall 24 being defined by a lip extending radially inwardly from sidewall 22 to form an opening 26 having a longitudinal extending central axis "C". Thus, mounting member 20 may be mounted around the mouth portion 13 of container 12. Mounting member 20 includes a pair of spaced apart opposed webs 30 that extend longitudinally thereof, that is, generally parallel to longitudinal axis "C". Each web 30 includes a hole 32 formed therein with each hole 32 being located at a lower end of its respective web 30. Moreover, each web 30 includes an axle pin 34 with axle pins 34 projecting oppositely from one another. With reference to Figures 4 and 5, it may be seen that each web 30 includes a shoulder portion 36 so that the space between webs 30 is smaller in dimension at the top of webs 30 then at the bottom thereof. Webs 30 along with holes 32 and axle pins 34 are operative to pivotally mount, respectively, actuator member 70 and cap member 90 as described more thoroughly below. Mounting member 20 is also provided with a plurality of radially outwardly projecting lobes 38 which are equiangularly spaced around the outer circumference of sidewall 22. Each lobe 38 is provided with a post-mounting bore 40 that is sized and adapted to secure an attachment post therein, as described more thoroughly below. When mounting member 20 is secured to container 12 in a mounted state, longitudinal extending central axis "C" is coaxially aligned with the central axis of the mouth portion of container 12. In order to help seal mounting member 20 against the rim of the mouth portion of the container, an annular gasket is positioned in opening 26. With reference, then, to Figure 7, gasket 42 is depicted and is in the form of an annular member that provides an inner seal portion 44 and an outer seal portion 46 that are separated from one another by a circumferential channel 48 that is sized and adapted to receive a margin of end wall 24. This arrangement is best illustrated in Figure 19. In that figure, it may be seen that, when in the mounted state, inner seal portion 44 is pressed against rim 14. Inner seal portion 44 is generally disk shaped in configuration while outer seal 46 is frustoconical in shape with an orifice 50 extending completely through gasket 42 to allow contents from the container 12 to flow outwardly thereof. As noted above, each of lobes 38 of mounting member 20 are sized and adapted to mount an attachment post thereto. A representative attachment post 52 is best illustrated in Figures 8 and 9. Here, it may be seen that attachment posts 52 each includes an elongated cylindrical shank portion 54 but includes at least one, but as illustrated, includes three fastening nubs 56, 57 and 58 which are both angularly and longitudinally offset from one another. A pair of fingers 60 project longitudinally from an end of shank portion 54 generally opposite nubs 56-58 with fingers 60 being spaced apart from one another and terminating in ears 62. Post 52 is constructed of a plastic material which exhibits resiliency so that fingers 60 may be deflected towards one another but, due to the resilient material, tend to spring back away from one another. As noted below, this facilitates mounting of attachment posts into the post mounting bores. To this end, as illustrated in Figures 10-12, each of post-mounting bores 40 of lobes 38 includes an internally radially inwardly projecting ridge 64 that forms a shoulder 66. Accordingly, when the end of attachment post 52 supporting fingers 60 is inserted into post mounting bore 40, as is illustrated in Figure 12, fingers 60 deflect so that ears 62 extend above ridge 64 while shank portion 54 is below ridge 64. Fingers 60 may spring outwardly away from one another so that ears 62 engage shoulder 66 to prevent withdrawal of mounting posts 52 from bore 40 unless fingers 60 are mechanically deflected towards one another again. Although post 52 may not be readily removed from bore 40, post 52 is nonetheless rotatable about a rotation axis "R". Attachment posts 52, as more thoroughly described below, thus allow attachment of mounting member 20 to an external rib or flange on the mount portion of the container. Mounting member 20 provides structure to mount actuator member 70. Actuator member 70 is best shown in Figures 13 and 14. In these figures, it may be seen that actuator member 70 includes a lever arm 72 and an actuator arm 74 that are joined at a vertex portion 76. Lever arm 72 is formed by a web 73 and a flange 78 which extends generally perpendicularly to web 73. Likewise, actuator arm 74 includes a web 75 and a flange 79 that extends generally perpendicularly of web 75 and which is formed as an extension of flange 78. A distal end portion 80 of lever arm 72 is provided with a knuckle 82, and a pair of slide pins 84 which project opposite one another on either side knuckle 82. Vertex portion 76 is also in the form of a knuckle 86, and a pair of hollow trunnions 88 extend oppositely from one another on opposite sides of knuckle 86. Trunnions 88 are sized and adapted to rotatably engage holes 32 in webs 30 of mounting member 20 so that actuator member 70 may pivot with respect to mounting member 20 about an actuator pivot axis "A", as is illustrated in Figures 2(a)-2(c). Further, it may be seen that each of trunnions 88 include a bore 89 to receive a biasing spring 110 as described below. Mounting member 20 also supports a cap member 90, with cap member 90 being best illustrated in Figures 15-17. In these figures, it may be seen that cap member 90 includes a circular cap portion 92 that supports a pair of spaced apart opposed wings 94 that are generally parallel to one another. Each wing 94 has an elongated slot 96 formed therein, and each web 94 further includes a hole 98 formed at an end thereof that is distal of cap portion 92. Holes 98 are sized and adapted to rotatably engage axle pins 34 on mounting member 20 so that cap member 90 is pivotally secured to mounting member 20 at a cap pivot axis "P" again as best illustrated in Figures 2(a)-2(c). Moreover, in order for actuator member 70 to pivot cap member 90, slide pins 84 respectively engage slots 96. Thus, rotation of actuator member 70 about axis "A" causes rotation of cap member 90 about pivot axis "P" due to the driving force provided by slide pins 84 acting on an end slot 96. Due to the offset nature of axis "A" and "P" along with the configuration of actuator member 70, the amount of rotation of cap member 90 is greater than the angular rotation of actuator member 70. Thus, for a relatively small angular rotation of actuator arm 74 over angle "a", cap portion 92 rotates a much larger angular amount, that is, a larger angle, "b". With further reference to Figures 15-17, and with special reference to Figure 17, it may be seen that cap portion 92 includes a disk shaped end wall 100 joined to an outwardly divergent sidewall 102 so as to create a frustoconical interior 104. A frustoconical plug 106 extends from end wall 100 in interior 104 so that the interior of cap member 92 between sidewall 102 and plug 106 creates a groove 108. Plug 106 is sized to extend into passageway 50 of gasket 42 as best illustrated in Figure 19. Further, groove 108 is sized and adapted to nestably receive outer seal portion 46 of gasket 42 when the cap member 90 is in the closed position illustrated in Figure 2(a). Here, it may be noted that it would be possible to construct mounting member 20 to include a plug structure and place the outer seal on in the interior 104 of cap member 90. In the exemplary embodiment, cap member 90 is biased into the closed position shown in Figure 2(a). To this end, a biasing spring 110 is provided with biasing spring 110 being illustrated in Figure 18. Spring 110 has a hook portion 112 that can engage an edge of mounting member 20 and has a prong portion 114 that can engage groove 89 formed in actuator member 70 adjacent a selected trunnion 88. Biasing spring 110 is sized to be received in bore 87 in knuckle 86 so that prong 114 engages groove 89. Thus, actuator member 70 is spring biased toward the first position shown in Figure 2(c) thereby correspondingly biasing cap member toward the closed position also shown in Figure 2(a). However, when actuator arm 70 is moved toward the second position shown in Figures 2(c), such movement is resisted by the restorative force of spring 110. When actuator arm 70 is released, this restorative force moves actuator arm 70 back to the first position and the cap member 90 into the closed position. With reference now to Figures 19 and 20(a)-20(c), it may be seen that attachment posts 52 are used to secure mounting member 20 onto the mouth portion 13 of container 12. As is illustrated in Figure 19, mouth portion 13 is provided with a flange 17 as is standard in the art. Mounting member 20 is positioned over mouth portion 13 with inner seal portion 44 of gasket 42 pressed against rim 14. Mounting post 52 may be rotated, as is illustrated in Figures 20(a) and 20(b) so that a selected nub, such as nub 56 engages flange 17 to prevent removal of cap member 20. Nubs 56-58 are provided at different longitudinally spaced locations to accommodate varying distances between rim 14 and flange 17 on standard beverage containers. Thus, as is illustrated in Figures 20(a) and 20(b), representative post 52 may be rotated so that different ones of the nubs may engage flange 17. In Figure 20(a), nub 57 engages flange 17 of a selected container while, in Figure 20(b), representative nub 56 engages a differently spaced flange 17' of a different container. Location of post 52 to the position shown in Figure 20(c), allows detachment of mounting member 20 and thus closure device 10 from container 12. An alternate alternative exemplary embodiment of the present invention is illustrated in Figure 21. Here, closure device 210 is adapted to be secured onto a container 12 by means of a different mounting structure. In this embodiment, the lobes 38 and attachment posts 52 are eliminated. Rather, mounting member 220 has a second thread structure 252 located on the interior of sidewall 222 with second rib structure 252 sized and adapted to engage the first thread structure 251 on mouth portion 13 of container 12. Thus, first rib structure 251 defines the external rib on the mouth portion of container 12 whereas, in the first embodiment, flange 17 defined the external rib. In any event, cap member 290 is again pivotally secured to mounting member 220 and is pivoted by means of actuator arm 270 that is also pivoted to mounting member 220 and that includes slide pins that engage slots in cap member 290, just as in the first embodiment. Inner and outer seal portions are again provided by a gasket 242 as in the first embodiment. From the foregoing, it should readily be appreciated that a user can conveniently employ the closure device of the present invention. To this end, the closure device is simply mounted over the mouth of a selected container, such as a drinking bottle and is secured so that the inner seal substantially seals the closure device relative to the bottle. The plug 106 of cap member 90 engages the outer seal member with the outer seal member being nested in groove 108. This substantially seals the cap member relative to the mounting member when the cap member is in the closed position. A user may open the closure member to allow access to the contents of the bottle simply by using a digit, such as a finger, to pivot actuator member 70 between the first and second positions. Since this is only a relatively small range, it is easy to do with a simple finger with the same hand grasping the container 12. However, due to the mechanical configuration, cap member 90 is pivoted completely away from the mouth of the container and does not obstruct the user's ability to drink from the container. When the user is finished, he/she simply releases actuator member 70, and the spring biasing action of spring 110 forces the actuator member 70 from the second position to the first position, which, in turn, moves the cap member from the open position to the closed position. Accordingly, the present invention has been described with some degree of particularity directed to the exemplary embodiments of the present invention. Il should be appreciated, though, that the present invention is defined by the following claims construed in light of the prior art so that modifications or changes may be made to the exemplary embodiments of the present invention without departing from the inventive concepts contained herein.