Implemented the following Colt45_2d methods:
-   loadSpriteSheet(imgUrl, jsonUrl, callback)
-   getSpriteSheet(imgUrl)
-   getSprite(spritename)
-   drawSprite(spritename, posX, posY)
-   __drawSriteInternal(sprite, sheet, posX, posY)

Refactored Atlas Examples:
-   02.Atlases-A.load-spritesheet.html
    Simple example of how to load an atlas
-   02.Atlases-B.draw-random-sprite.html
    Load an atlas and draw a random sprite
-   02.Atlases-C.animate-sprites.html
    Load an atlas, group sprite animations, and animate them all on screen
    This is Jose's original example, minus methods now encapsulated in colt45-2d