Au Naturel Resource Pack

- Added and adjusted spawn frequency of Yung's better nether fortresses to be roughly double the defaults.  Likely interacts with sparse structure changes, so still shouldn't be an issue in practice.  But if it is, eh, someone tell me, because I'm not exactly expecting many people to be able to advance that far in a standard server or world_gen game to where they're actually in the nether, and once you're there it's supposed to be hellish.  But now it's here because it provides a possible end-game goal if you're really masochistic and want such a thing.  Try to craft the beacon you filthy casuals!