Make minimally playable (using the test map.)

This is neither here nor there.  Do with it what you like, or tell me to zark off, or whatever.

These are the changes I had to make to get the game up and running for me:

* copy `TEST_MAP` to the default map file (which is empty and thus invalid JSON)
* ensure there's an `npcs` field in the game data
* adjust the camera size to fit the test map

I suppose I could've composed some map data that was big enough and had some NPCs in it, but I haven't figured out the map editor yet and I didn't want to fiddle directly with JSON.