Added gridwise movement.
Refined player movement.
Actor pickup and dropping now works.
Monsters now have a little AI. Tiles with items crank up cost.
Doors now block monsters but not humans.

Monsters now avoid obstacles if possible, but otherwise "grind" them.
Items can now be "ground" and killed.
Actors can now have lights that they create, maintain, and attach.
Added cracks, debris particles.