Merge pull request #771 from pandamicro/develop

Update submodules
Update html5 engine
Merge branch 'develop' of https://github.com/cocos2d/cocos2d-js into develop
Upgrade html5 engine
Issue #5907: Add cc.view.g|setTargetDensityDPI
[Cocos2d-JS 3.0 Release] Add docs