I have several questions related to procedural structure generation (piece-wise multi-chunk structures like Strongholds, Nether Fortresses, and many Twilight Forest structures, not single-pass isolated structures like dungeons, jungle temples, and anything generated in an IWorldGenerator).   How do I go about adding my own kind? I assume I extend MapGenStructure, but how do I register it? ChunkProvider classes seem to hardcode what generators they use, with no obvious Forge hooks aside from a