Merge pull request cocos2d#890 from pandamicro/develop

[3.1 release] Add docs and update h5 engine

Merge pull request cocos2d#833 from pandamicro/develop

Update plugin-x

Merge pull request cocos2d#781 from dingpinglv/develop

Updates cocos2d-html5's reference.

Merge pull request cocos2d#748 from pandamicro/develop

Fix issues

Merge pull request cocos2d#693 from dingpinglv/Iss5781_V3rc2

Closed #5781: update the reference of cocos2d-html5

Merge pull request cocos2d#551 from pandamicro/master

Release #5636: Update docs and cocos2d-html5 ref

Merge pull request cocos2d#453 from dingpinglv/master

Issue : update the reference of Submodule