pygments lexer support for mkdocs highlighting

[jippi]

Hey!

Thanks for a ✨ fantastic ✨ project; very very cool to use and easy to extend - been quite a fun experience implementing it into jippi/scm-engine!

I'm using mkdocs (and mkdocs-material) to build my documentation, and noticed expr is not a supported language in pygments, the tool that mkdocs use for code blocks.

It would be fantastic if it could be supported so the documentation generated looks ❤️ pretty ❤️ and easy to read.

Thank you,

[antonmedv]

Nice idea! Will try to see on how to add support in pygments for expr.