Examples: Draw bpfsnake with pygame and steer it from the window

A pygame window takes the keyboard from the terminal, so the pty_write
probe would never see a key. Python writes the key code into the state
map instead, one queued turn per tick, ignoring reversals. The board
grows to 20x30 with food anywhere inside the walls, and the snake to 32.

Author: varun-r-mallya