ArtifactOfVoid

Adds a new gamemode via a new artifact.

Still rough around the edges, but 0ddlaw wanted me to release it, so here it is!

The game's normal levels become more like the Void Fields, while still retaining something of the normal gameplay loop. Four Void Rifts appear, each adding new monster types and items to the pool when activated. Once they are all completed, the teleporter event can begin.