Switch from `commonmark-hs` to Pandoc for parsing Markdown

[srid]

But emanote uses commonmark-hs (from same author) to parse Markdown. I'm okay with us switching to parsing with Pandoc. The Wikilink extension, as well as the HashTag extension, would be the main thing to port over.

Originally posted by @srid in https://github.com/srid/emanote/discussions/250#discussioncomment-2145470

[srid]

Should measure the performance impact.