Initial Release

- Added the totem-of-undying immortality exploit from Spoke's Purgatory Prison video.
- Players can be granted "immortal" status, intercepting lethal damage and auto-equipping a Totem of Undying.
- Added /unstable immortality add <player> and /unstable immortality remove <player> commands.
- Added unstable.admin permission to control access.
- Immortal player list now persists across server restarts via config.yml.