Flowmark

- Avoid overly aggressive en dash rewriting that breaks URLs
- Small wrapping fixes: Avoid wrapping sentences on "p.", "i.e.", etc.
- Improved menu labels

- Add footnote id normalization command
- Bugfix: Some commands (heavy cleanup) did not activate the plugin

- Turn on footnote support so footnotes are handled properly
- A few additions to "heavy cleanup" mode

- YAML/TOML frontmatter now supported 23
- Fix two (relatively rare) wrapping bugs with long links that resulted in extra newlines or missing space 10 27

- Expose sentence split methods `sentence_split_regex()`, `first_sentences()`, and `first_sentence()` convenience methods.

- Minor linting cleanups.
- Build system/docs updates.