Added the rest of Secret Level 1!

Added compatibility with Goganidze's extension of the mod, allowing for full 3D looking and firing!
(requires REPENTOGON)

(also added a whole bunch of other stuff since I'm too lazy to separate my working build with the demo build :p)

All member variables of the Player are now properly reloaded when dying/respawing or loading a new stage!

Added a photosensitivity mode that disables pickup flashes and smooths out the textures to prevent flashing from rendering at medium distance. It's a bit of a hacky solution, but it is toggleable, and I can always adjust it later if I find a more elegant way to prevent flashing.

Changed the name. I admit it's not really "DOOM" right now, but I assure you that it will be closer to DOOM by the end of it all :p

- Fixed a bug that would cause a black screen if the player died, returned to the title screen, then entered the options menu.