A new lighting system

This update adds proper lighting to the game, which makes the environments look a lot better and also allows me to play with dark areas and blinking lights when creating the levels and encounters, just like the original DOOM games do. 

Here are some screenshots of what the game looked like before the update:

And what it looks like after the update:

Other changes:

• Due to an issue, one of the levels had to be removed. It will be re-added in a later update
• The geometry of the level "The Graveyard" has been slightly modified. Some new rooms have also been added
• Completely overhauled all the encounters in "The Graveyard"
• The player now loses all momentum after teleporting, meaning it won't slide by itself anymore
• Some demons now create light when performing certain attacks
• Weapons now create light when fired

Bug fixes:

• Fixed an issue that caused all projectiles to deal double the intended damage to the player
• Fixed an issue that caused dead demons to be able to revive even if an Archvile wasn't present anymore