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
* Changed the names of some of the functions
* Added functions for setting and returning the projection matrix of the active camera
* Added a function for getting the 2D screen coordinates from a 3D vector
* Added documentation for all the new functions
