Way to use .ldtk file at compile time only

[zommerfelds]

From what I'm experiencing, it seems like the .ldtk file doesn't actually need to be included in the release. In my case I'm loading resources in a PAK file. This library still works if I compile with the full file but only provide an empty .ldtk in the PAK at runtime. So I'm wondering if we should:

1. Not try to load the .ldtk file at runtime if data is already there. What is the file used for at runtime?
2. Provide a way to map the relative path to your resource base path in the editor. For example if I put the .ldtk file in the src directory and reference a tile set in a sibling res directory it will be saved as "relPath": "../res/tileset.png". I will see all tiles in the editor, but when running the game it will fail because the assets are not loaded relative to the src directory.

If you are interested I can try to look into making a PR, but wanted to have your input first. It's probably not as simple as I'm imagining. :)
Thanks!