Update 4 (probably)

Update 4 (unless I'm mistaken):

Added enemy AI.

Added game difficulty setting.

Tweaked some damage parameters, etc.

And probably some other stuff which I'm forgetting.

---------- Remaining TODO ----------

=> Edit the One Page Game Design document according to the new game design.

=> Design a level:

- Write a Spawner class.

- Create spawn points for the pickups, enemies.

- Weapons will have fixed spawn points.

- Tie the spawner's timers with the Game Difficulty.

- Higher difficulty = quicker enemy spawns.

- Higher difficulty = slower pickup spawns

=> Make pickups:

- Don't forget to edit PlayerStats when they're picked up.

- Let enemies pickup pickups, if they happen to walk through them.