Automate SVG rendering in MkDocs

[aabounegm]

Removed the hard-coded SVGs from the markdown and instead wrote a tiny MkDocs plugin (hook) that renders them from the fenced code blocks. One shortcoming is that the RegEx used for detecting code blocks is too simple and doesn't cover all possible markdown syntaxes. Additionally, this depends on the existence of the rzk executable in the PATH.
I also added a step to the GitHub Action to install rzk since MkDocs now depends on it for rendering.

Additionally, I modified the GH Pages publish steps to be single-commit to optimize the git repo size (in the future, I would recommend using actions/deploy-pages instead, which does not depend on having a gh-pages branch)

[fizruk]

Thank you! Looks good modulo minor comments which I left above.