Cheats:

 Pause the game using [Pause], then type one of the following codes to
 unpause with the new option:

 IAMGOD      - God mode ON/OFF
 GHOST       - Wall collisions ON/OFF (No-Clipping)
 ALLGUNS     - Free ammo for all weapons
 HIDEENEMIES - Enemies/Objects ON/OFF
 FPS         - Show frame rate