More Mystcraft

This is an beta release. Do not use with worlds or saves you intend to keep.

 Added a couple of options for Mystcraft's scattered libraries: disable them entirely, or upgrade them cosmetically. Both options are available in the config.

This is more of a hack than anything else because the libraries are hard-coded into Mystcraft dimensions, but it should work pretty well. Disabling the libraries may be obvious in locations where they have altered the terrain. Leaving libraries enabled but disabling the cosmetic upgrade will cause 0 slowdown because the world generator used to replace the libraries won't even be registered.