Mountain Mineshafts

Mesa mineshafts now generate in mountains.

These will replace the normal mineshafts. You can rarely find them peeking out of the base, giving you easy access to the emeralds and other ores that generate there. Just watch out for silverfish...

I have also tweaked mineshaft generation as a whole - They are now spaced out by 4x the amount, but are twice as likely to appear at possible instances. The actual structure has not changed.