Animation became generic FrameAnimation.

Usually frame animations will consider sprites, but as that it no
strict requirement, I just made the class able to handle frame object
of any type.
Time docs.
Implemented Scene and SceneProxy classes.

The names Scene and SceneProxy seemed to better suit their purpose than
State and StateMachine. The latter names were lying in the sense that
they were too generic.
Added unimplemented methods to audial classes.

I was starting to think about how these classes could be used together
in order to allow an application to play sounds.
Made Looper class simpler.

Now has a constructor which requires a target frame rate.
Added unimplemented methods to visual classes.

Just thinking about their implementations.
Docs for spatial classes.
Empty Entity class with docs added.
Re-added Game class from old code.

Not quite done with it yet.