[Cocos2d-JS] Improve doc for v3.0 RC3 release
Merge branch 'master' of https://github.com/cocos2d/cocos-docs
Merge pull request #480 from pandamicro/master

[Cocos2d-JS] Improve doc for v3.0 RC3 release
Merge pull request #479 from gloryming/master

updated js v3.0rc3