Improve naming convention

Some naming convention improvement.

### 1. cocos_2d & box_2d to cocos2d & box2d
IMO, *cocos2d* & *box2d* is proper name.
I think this is for more readability.

### 2. macro prefix bbp to jbp
About this https://github.com/rubymotion/Joybox/pull/1#issuecomment-15674521