Multiple characters and perf stats

Tiny update this time.

Support for more than one playable character

Print out performance stats in top left corner

TICK is the number of milliseconds for main update loop

BUFF is when we process our graphics buffer and create the SDL commands to draw it

REND is when SDL actually renders to screen (it’s so high because of VSYNC)

The first value is actually quite high right now, because I’m very wasteful and calculate shadowcasting and A* every frame even when nothing changes.