Suggested solution for supporting custom labels on file includes

Here's an updated suggestion on how to support this:

https://github.com/aaslun/Arlima/commit/24ac91b0cd32ae862c7df01c7644f5415bcf4ac3

The custom label has to be assigned somehow when the file include is registered with Arlima, and in an attempt to avoid an implicit solution (using the arlima_file_args) I propose using array keys for the custom labels in the arlima_article_includes filter. Will it suffice?