Documentation for World and Biome generation #66

i found that there's no documentation whatsoever about world- and biome generation. i found a few topics at the forge forum but all those are using the BiomeGen class, which isn't available anymore. rather there's a Biome class which i can extend from, but no idea how i register a new biome (theres Biome.register and GameRegistry.register).

also, would be nice to know how to add a new biome to the default world, and even nicer if it could be selected in the "create world" advanced dialog of the client (where you can set of which biomes the world should be created, e.g. "All", "Ocean", "Hills", etc