Finished documentation on sprite physics and joints
Fixed some bugs in sprite physics
Added safety checks for joint types
Added code to free up joints when a canvas is destroyed
* Rewrote the actor animation system to work like sprites
* Renamed a few functions
* Added DeleteSpriteAnimation() and the delete queue to sprites
* Removed transitions for the time being (they don't seem to work in irrlicht right now
* Added PreUpdate() function
* Added documentation for name changes and new functions
