Bugs solved when removing components

On Entity.java, the component wasn't removed, just the componentBits was
cleared.

On Engine.java, when the component removal signal was dispatched, the
familyBits was set, not cleared
Merge pull request #6 from adeluiz/master

Bugs found on Component removal
Merge pull request #4 from siondream/master

Adds Entity and Component pooling
Added Apache 2.0 License notice.
Modified README to mention license.
Update README.md
Adds EntityListener
Adds EntityListener to BasicTest