Add actor subclass and related asset loading assist tools

[pushfoo]

Closes #14 , Closes #7 , Closes #6

The major changes are:

1. We have a setup.py and the way to use it is documented in README.md
2. Tools for loading numbered assets from folders are now working. As long as you follow the naming conventions, the animation state atlases will just work.
3. Actor is now more implemented and backed, even if it's somewhat threadbare. Both cops and the gorilla use it.
4. The gorilla loads and uses the animations you made.

Even if we radically change our game direction away from the planned design, the groundwork laid by this should let us prototype quickly with arbitrary animation states allowable. Also, The setup.py file should work just as well from a .zip we cut for release as from git.

The file naming conventions that work with load_asset_group and preload_entity_texture_table in asset_loading.py are probably most important things to pay attention to. As long as you name files with the naming pattern in the cop and gorilla folder, walk and still states should just work for actors. Going from animated, moving characters to patrolling cops is probably pretty easy at this point. The timer exists for purposes just like this.

I'm not too attached to the moving property in actor and we could get rid of it or rework it, including moving more functionality related to it into Actor.

I'll post more thoughts in the server.

[pushfoo]

In the interest of getting something playable, I'm merging this.