Regions are no longer a thing

Map regions have been removed, so worlds are just a nice big 2D array
instead of a needlessly complex 4D array.

Collisions are now dealt with using a collision map that's separate from
the tile data. Pretty successfully moved collision testing to the Map
class as well; Entity's chkSolid() only has a shortcut to it that
converts vectors to map indices.

Caching still makes the whole game jug a bit every few ticks; need to
separate simulation from display somehow. No caching means really big
chugs every now and then though; no idea what's going on there.

May work on Entity regions soon to speed up area of interest updates.
O(n) is a bitch.