Added a bunch of new stuff, but this update is mostly changes.

New stuff:

• Added new enemy: Wraith
• New firing mode: Shotgun (swap firing modes with Q)
• Proper skeleton death sounds
• Now you summon waves by shooting the bell in the tower.
• Enemies have a chance to drop health pickup (healing value decay to 1 over time)

Updates to:

• Skeleton behaviour
• Post processing effects
• Options menu
• Weapon sounds
• Overall look of the game