FIXED:
- Fixed an error when reloading while there were ongoing classes.
- Fixed issue where players would not be teleported to the main spawn when the lesson was ended.
- Fixed an issue where every room's 'teleportation' value would standard be saved as false.
- Fixed an issue where players would constantly join again and again when walking in a room with walking mode enabled.

ADDED:
- Nothing

CHANGED:
- Removed a lot of redundant API methods and changed some methods in the PlayerData class.
- All parameters must now be NonNull unless specified differently.
- Some methods will now be annotated as Nullable to be more specific.
- Recoded the whole project. There is still a lot of optimization to do, but I think it's going in the right direction. Please notice that this update is experimental and may cause issues.