Adds component pooling
Brings Pool, Pools and ReglectionPool from libgdx utils package
Adds entity pooling
Adds missing documentation
Updates tests
Makes Entity and Component pooling support independent from Engine.
Adds PooledEngine.
Adds Engine#getSystem() method
Adds Entity#HasComponnt to not have to check the componentBits manually
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