[Cocos2d-JS] Improve beta docs
[Cocos2d-JS] Add change log and release note for rc0 release
[Cocos2d-JS] Upgrade AssetsManager doc
[Cocos2d-JS] Rename bakeLayer folder to bake-layer
Merge branch 'master' of https://github.com/cocos2d/cocos-docs
[Cocos2d-JS] Improve beta upgrade guide
[Cocos2d-JS] Add upgrade guide for 3.0 rc0
Merge pull request #375 from pandamicro/master

[Cocos2d-JS] Prepare for Cocos2d-JS v3.0 RC0 release