[Feature Request] Support Org-Roam's heading nodes

[PRESFIL]

Description

Org-Roam has heading nodes (like in logseq), so multiple nodes can
live in the same file. Because of this, pandoc runs multiple times on the same
file and creates duplicates in output/ directory that can be found using
jdupes.

Also likely that links to such heading nodes are invalid - they point to a
file and not to a place in the file.

[goshatch]

Hello! Thank you for the feature request, this is a real problem that I've run into myself.

Unfortunately I don't currently have much free time to work on this, but I'd be happy to review a PR introducing this fix, if you (or anyone else) would like to take it up.