Feature #3942: Refactor singleton classes to objects in Extension
Refactor #4240: Refactor purgeXXXCache to _clear which won't be supported in JSB
Merge branch 'develop-3.0' of https://github.com/cocos2d/cocos2d-html5 into develop-3.0
Update samples
Merge pull request #1629 from pandamicro/develop-3.0

Feature #3942: Refactor singleton classes to objects in Extension