Ticket #8: First commit playing with TexturePacker stuff

not that much for now !
ticket #8 : added a function to create a sprite using the Atlas, and other small improvements

still pretty draft anyway :)
small changes here and there, nothing significant today :(
minor changes
ticket #8: added trimming support
changed the sprite rectangle color to green when debugging is enabled
Added more details on the `anchorPoint` property usage + fixed indentation
ticket #8 : use the entity anchor point to define the renderable positioning

* default position is now around the entity center
* platformer example update to bottom aligned (0.5, 1.0) the sprite to
the entity
Ticket #8 : added animation support, through the `createAnimationFromName` function
ticket #8 : optimized memory usage when using animation (thanks Jason for the code review!)
ticket #8 : fixed "default" angle not being applied

this is still broken though, as once rotation is enabled in
TexturePacker, sprite position is off .
ticket #8 : updated the platformer example to use TexturePacker sprite for all entities
ticket #8 : fixed default angle value when creating sprite objects.
ticket #8 : added proper example(s) in the documentation
ticket #8 : added a local constant for (PI*2) to avoid repetitive/unnecessary calculation