slow down player slightly, fix spacebar firing issue

make sure player only enters manual mode if a direction key is pressed,
i.e. you should be able to move with the mouse and fire with the spacebar
resize board with window
big refactor, initial HUD
various tweaks

* wrap text in HUD when necessary
* DRY up text logic
* increase pursuit threshold w/ each gunshot (gradually shrinks back)
* make zombies keep pursuing for a few seconds after player escapes
  threshold