TODO (in descending order of wishlist priority):
- README project information and details
- wall and ceiling collision
- add hurtbox to player
- monster class
- follows player
- has health points
- handle hurtbox interaction with monster class, observer class
- add shooting mechanism (add new controls to KeyHandler) with hitbox
- world screens to implement world traversal
- portals, add portal usability to KeyHandler
- platform data location
- implement proper player-platform collision
- refactor Game, KeyHandler, Player class into singleton