Added newly created SpriteStage and SpriteContainer classes to introduce an agressively optimized WebGL renderer. Also a few other tweaks to Stage to allow for layered stages.
Merge pull request #409 from trevordunn/master

Added newly created SpriteStage and SpriteContainer classes to introduce WebGL support to EaselJS
Updated NEXT documentation and libs. New NEXT version contains updates to support WebGL classes, but NOT the WebGL classes themselves.

Signed-off-by: Lanny McNie <lanny@gskinner.com>