v0.6

Changes:
- World generation is now entirely handled on the server. The client spawns the server in a separate thread, and the server is responsible for saving and loading worlds.
- Added a menu to choose which world save to load, or to specify a name for creating a new world.
- Added keybinding customization in the settings menu.
- Implemented multithreaded meshing and multithreaded world generation.

Full Changelog: v0.5...v0.6