Roundabout: The JoJo Mod

- Added 3 new mobs in preparation for wip gold experience (ty superguy!), made to fit into vanilla
  - Snakes! They are neutral, if you mess with them you can get poisoned. They drop their skin which can make snake skin boots, which step silently. You can also make snake oil which can trick villagers to get you a free trade (with big consequences)
  - Butterflies, they are ambient mobs much like bats
  - Piranhas, they are neutral fish that inflict bleed. If mobs are bleeding, they are aggressive to the mobs. They have a raw and cooked version as items and can be put in buckets
- Many bugfixes (see tracker and github)
- Major work on WIP skins
- Some internal improvements
- Please PVP test purple haze, it is almost ready for release ^^
  - So is 20th century boy