A Jose Conseco bat? Tell me you didn't pay money for this...

Added input state constants to constant.coffee
Added killZombie() method to GameState
Added input state display to the gui
Expanded input handling in Player
- Weapon keys now enter their own input states
- Bat is fully functional; zombies can be killed!
Added killed field to Zombie
Zombie now removes itself from the scheduler if killed
Reference: https://www.youtube.com/watch?v=cg6udLhqxxc