Convenience func for Markdown footnotes.

Merge pull request #2 from jlevy/new-html-tags

Improved html tag find/replace with selectolax.

Upgrade to flowmark v0.5.3.

Add missing exports.

Add attrs support to `div_wrapper`.

Minor cleanup to allow None as DiffFilter.

Linting/typing fixes.

ruff formatting+linting.

Disable mypy error. poetry up.

Update docs and flowmark dep.