wasd / arrows: move
      mouse / ijkl: headbutt
      space: bullrush
    

      tab or []: select value
      -/+: modify by 1
      shift -/+: modify by 10
      alt -/+: halve or double
      /: filter values
      delete: clear override
    

      shift p: pause game
      alt p: step one frame
    

      shift l: console.log state
      shift r: reset to initial state
      shift g: show grid