v0.4.10+1.19.4

What's Changed

• Added support for creation of custom worlds using own class extending RuntimeWorld.
• Added support for unloading of worlds without file deletion.
• Fixed issue where server would sometimes crash when adding/modifying worlds.
• Fixed bug where world options/settings were saved in level.dat, making them auto-load without required data.
• Extra protection for duplicate entries @PinkGoosik in #25

Full Changelog: v0.4.9+1.19.4-rc2...v0.4.10+1.19.4