WadSmoosh 1.31

A minor update:

• Add the "Ultra-Violence+" skill level from the Unity ports, which adds Fast Monsters and the multiplayer-only weapon spawns to Ultra Violence difficulty for additional challenge.
• Plutonia credits update thanks to Shockwave_S08: Dario and Milo Casali are credited individually for the levels they were each the primary author of, since more detailed credit information has come to light.