0.3 - Polishing update.

• Rework world generation.
• Delay firing projectiles.
• Fix zombie hitbox position.
• Fix exit appearing near spawn.
• Fix projectile hitboxes staying in place killing zombies.
• Fix unbalanced level generation.
• Balance the difficulties, easy now isn't peasy.
• Make the spike hitbox narrower.

Fun fact: I only noticed the entity collision code is different from the player when I was trying to fix an unrelated entity bug. Fun!