Swap SCREEN_ constant for WINDOW_ (slightly more descriptive)
Relate MAP_ constant directly to WINDOW_
Remove magic number (TILE_WIDTH), raise it to 20 to shrink map size
Refactor direction code; change snake.parts to snake.body
Refactor snake direction code: kill running over yourself bug
Add choice of colors to config.yaml for map, text, border
Add snake and rabbit colors to config