feature: Option to also display isolated nodes (not called, not calling)

[pawamoy]

I'm experimenting with Code2Flow to automatically inject call graphs into my docs pages for each internal module. Some of these modules declare several things but that don't have any interactions, so for these modules, the generated graphs are empty. I was wondering if it would be possible to add an option to say "pick up and render nodes even if they are not called by anyone and don't call anyone"? I'd understand if you consider this out-of-scope since Code2Flow was designed for call graphs, not for "more generic" diagrams 🙂