v2.1: Merge pull request #17 from FaceDeer/ground_covers
Accumulated tweaks and bugfixes, as well as several new minor features:
- New ground cover types
- Guardian statues in the Underworld
- Glowstone veins in the Primordial layer
- Limit fire spread in the Primordial layer
- hunger_ng support, with a few new edibles in Primordial layer