Add a cc.ResLoader Class

In my opinion , A game base on web-browser should have a common resource manager during the resource lifecycle ( such as load,cache,and destroy ) . It can grow lots of superiority on game resource version management , network logging , resource loading queue and so on .

I want to add the "common resource manager" in these step :

1. add a cc.ResLoader Class ( such as this pull request )
2. replace cocos2d-html5's loader/ajax code with my cc.ResLoader
3. add a flexible ResourceManager Class

If cocos2d-html5 core team agree with me ,please merge my pull request , thanks