Support for citation syntax (similar to MultiMarkdown)

[ShredderWalnut]

Describe your feature request I heavily rely on MultiMarkdown's citation syntax. I have different use cases for citations and footnotes: one for citing sources, and the other for additional info added by me.

I see that FSNotes uses cmark, so I imagine it would require much dev work to implement my request. Searching in this repo returned no similar requests, so perhaps very few people need the feature like I do, but I do hope you'll consider implementing it in the future.

Thank you for your time and this amazing piece of software, Oleksandr!

Additional context Add any other related information here. macOS or iOS?

I'm new to FSNotes and plan to use it exclusively on macOS.