Added

- Advancements — a tab of their own and three challenges: eat a sunstone
  apple, catch fire from your own splash distillate, and *Tempered* for riding
  out the third order in full. The tab is visible from your first join.
- Tempered comes with rules: no fire resistance, no golden apples, no water,
  no armour. Burning costs more health than a player has, so regeneration
  is the only way through.

Changed

- The third order now lasts 33 seconds instead of 30. The duration is tuned
  to the advancement: burning costs 35 health, Regeneration II gives back 17
  over its 22 seconds, and twenty leaves you on exactly one heart.