Markdown-svgbob

- fix requirements specifier

- Upgrade svgbob binaries to 0.5.5

- Upgrade to svgbob 0.6.2 for Linux
- Packaging with lib3to6==202108.1048

I can't get newer binaries for windows or macos, contributions to
svgbob would be welcome. https://github.com/ivanceras/svgbob/issues/35

- Fix: False positive warning due to 'toc' extension.

- Fix: Close file descriptiors of Popen
- Add support for blocks with extra backticks

- Fix related to [14](https://gitlab.com/mbarkhau/markdown-katex/-/issues/14): Since `Markdown>=3.3` support for [Markdown in HTML][md_in_html] was broken.

[md_in_html]: https://python-markdown.github.io/extensions/md_in_html/