Folia compatibility

[SlimeDog]

🚩 We should do nothing until Folia reached a stage where the core functionality isn't bug fix du jour, and core plugins -- ProtocolLib, Vault, PlaceholderAPI, LuckPerms, etc. -- have been updated to actual releases. I'm not going to build all the prerequisites from branched dev sources.

If Folia becomes a significant number of servers that we need to support:

• [ ] Add folia-supported: true to plugin.yml
• [ ] Verify plugin operation
• [ ] Fix any errors
• [ ] Post compatibility
  • [ ] SpigotMC
  • [ ] Hangar
  • [ ] README.md

See PR https://github.com/SlimeDog/EntityCount/pull/11

[SlimeDog]

Re-open when Folia is ready for primetime.