New optimization update! (3.1.0) 
This update focuses on significant performance optimization and revamping separate level files.

Features
- Projects/levels can now safely be nested in prefab and prefab variants
- Optimised many internal systems to make importing much faster
- Added a new "Dependencies" section to both the project and level importer inspector to display what will reimport the LDtk Project/Level when a dependency is modified  
- Significantly improved support for separate level files
  ↳ Only modified level files will reimport instead of the project and all levels, resulting in quicker import speeds when applicable
  ↳ Only the dependencies involved in a particular level will reimport the level instead of involving all possible dependencies (Entities, IntGrid tiles)
  ↳ Level files are now imported simultaneously in parallel, resulting in faster import times when reimporting multiple levels. 
    ↳ Available in Unity 2021.2 or higher. Enable parallel importing at `Project Settings > Editor > Asset Pipeline > Parallel Import`
  ↳ For speed reasons, using separate level files is now highly encouraged moving forward for any moderately sized game project

- Added safe type checking and support for external enums
- All debug logs will now only show a maximum of 50 duplicates, and have coloured text in the console
- Sample scripts now support the new Input System package
- Added a new static collection of all enabled level components to simplify accessing levels in runtime

Changes
- Changed how the project importer manages assets
  ↳ All artifact assets generated by the project importer are now indexed, resulting in significantly quicker speeds when accessing sprites/tiles 
    ↳ This was the most significant performance consumer and was exponentially slower on larger scale projects

- Updated the Newtonsoft Json package to 3.0.2
- Changed max displayed artifacts in the artifact assets inspector to 50 for performance reasons
- From the LDtk Preferences, removed the option from logging import times and replaced it with exporting profiler details
  ↳ Alternatively, import times can be viewed from Unity's Import Activity Window
- Removed a MenuItem command that was accidentally included in the package
- Outdated JSON versions of LDtk projects will no longer be imported to enforce safety
- Many other small internal fixes and tweaks

Fixes
- Fixed some tiles not scaling properly if their gridSize was different from the pixels per unit
- Fixed an important bug where tiles would not scale or space apart correctly when multiple tile layers are involved
- Importing backup files for separate level files is now ignored in addition to project files
- Fixed the ILDtkImportedLevel not invoking when no level fields were defined
- Fixed the level background position being incorrect when set to "Not scaled" or "Fit inside"
- Updated samples
- Assets like entities and IntGrid tiles assigned to the importer where their definitions than were deleted, are now properly cleared out from the importer to not result in unnecessary dependencies
- Added an additional texture size check if the imported texture size was too small to prevent a misleading tile slice error
- Many other minor fixes and optimizations

Breaking Changes
- When separate level files are enabled, the project hierarchy does not build levels anymore and will be an empty hierarchy. Use the imported separate level GameObjects
- The json asset artifact will no longer have its level's layer instances available if using separate level files for performance reasons. Instead, deserialize the specific separate levels to get a level's data
- Removed the initial `Null` value for every autogenerated enum. This may shift indexes
↳ This was originally intended for the 3.0.0 update but was not applied until now