H5: Changelog v3.0a - update document urls
H5 v3.0a: Singleton objects doc added
H5 v3.0a: Singleton objects doc ref added in upgrade guide
Merge branch 'master' of https://github.com/cocos2d/cocos-docs
Merge pull request #178 from pandamicro/master

H5 v3.0a: Singleton objects doc added