MMR - Moog's Mineshafts Reimagined

\### Added - Snowy mineshafts now generate a surface entrance building that descends into the tunnels, with its own entrance loot including dyed and enchanted leather boots for crossing the mineshaft's powdered snow. ### Changed - Snowy mineshafts now spawn on relatively flat terrain so the surface entrance sits cleanly, and their underground pieces are buried rather than carved into the ground.