Merge pull request #730 from dingpinglv/Iss1615_WebGLRendering

Issue #1615 Implementing WebGL rendering
Issue #1615 implementing cc.DrawNode, cc.TextureAtlas and cc.SpriteBatchNode for WebGL
Merge branch 'webgl20' of https://github.com/cocos2d/cocos2d-html5 into iss1615_WebGLRendering