dev\perf: in draw() only iterate over on-screen map cells. (Previously we iterated over, but didn't draw, every cell in the map.)
perf: only change canvas color when required. This gives a tiny 1% perf improvement
dev: unused line
Hide touch controls when a keyboard key is pressed
Smooth camera when player falls a long distance. (The camera now pans at the same speed as the player falls, so there's no jerkiness)