Move mouse init to `Graphics::new()`
Default tilemap impl.
Added tilemap.
Make tile-size public & reduce screen resolution.
Tilemap draws row @ ~320px

* We have to use multiple sprites b/c I broke out set_position() and draw()
* (Should probably merge them so I can reuse single sprite.)
Add little obstacle course to the test map!
Merge branch 'feature/tile-map'