Flowmark

- Minor improvements to footnotes-after-punctuation option

- New menu option: Normalize footnotes to follow punctuation
- Remove `{ul}` markup as part of heavy cleanup option

- Always use fenced blocks. (This is clearer and easier to copy-paste and change language info.)

- Add math support ([remark-math](https://github.com/remarkjs/remark-math) syntax)

- Full remark updates and big code cleanups thanks to wooorm !
- Now current with unified+remark dependencies
- Improved footnote support thanks to the new [remark-footnotes](https://github.com/remarkjs/remark-footnotes)
- Improved testing and developer docs
- A few very small formatting rule changes: Newline now consistently before item elements. The rule below table headings now is now of the form `| - | - |` etc. (not dash padded).

- No longer pad tables. Many tables are wide and this seriously impairs editability.