Split Allegro CFFI bindings to a seperate package

Allegro Package
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All of the Allegro bindings were mixed in with the stuff pertaining specifically to your game. I figured it would be easier to work with for other projects if the Allegro stuff was split off into its own package, which could then be `:USE`d in whatever package you like.

I'm not incredible familiar with your codebase, so there might be some stuff in the `ALLEGRO` package that you think should be in the `GAME` package, or vice versa.

I'm also not incredibly familiar with the Allegro bindings you've put together, so I exported pretty much everything. There might be some stuff there which is internal and shouldn't be exported, so feel free to remove a bunch of exports if you like.

The projectile-demo.lisp demo doesn't seem to work after my commits, but as far as I can tell it didn't work properly before them either. I figured it was safe to assume you don't mind terribly about it not working? If you do, let me know and I'll try and fix it and send another pull request.

General Cleanup
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I also cleaned up the repository a little bit; there were a few files that shouldn't have been added to the repo (allegro.fasl and allegro.lisp~), so I went ahead and removed them and added a .gitignore to exclude them in the future. The issue you talk about in the README about `MAIN` not being an external symbol was because it wasn't being exported, so I exported that from the `GAME` package.