Adds DOOM difficulty names to the game.

• I'm Too Young To Die | Normal
• I Just Want To Kill | Hard
• Hey, Not Too Rough | Very Hard
• Hurt Me Plenty!| OVERKILL
• Ultra-Violence | Mayhem
• Nightmare! | Deathwish
• Ultra-Nightmare | Death Sentence

One-Downs are now Hardcore.
Contains Wolfenstein descriptions.