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
* Finished working on tiling
* Changed how sprite layers work. Sprite layers are now not confined to the limits of the actual canvas but instead will decide where to draw each sprite based on the canvas offset and the sprites location
* 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
* Added collision callback
* Set sprite density to 1 by default
* Added default frame value of 0 on frame resize
* Changed defaults for sprite fixture
* Made changes to some of the animation functions parameters
