Feature Request: Full Mermaid support

In order to use this for code planning and code descriptions I need to enhance this with Mermaid support. (I also plan code syntax highlighting.) I'm doing this on my own branch. The question is if I should upstream it?

First pass I got it working with pure python. However, it was limited and couldn't handle the full modern Mermaid suite of graphs, in particular the class diagrams. And while sequence diagrams are great I don't see a point in Mermaid to have another source of flowcharts, graphviz handled that better. So my second pass I'm reluctantly adding a npm and chromium (headless) reliance so I can use the latest Mermaid.js. This is still in progress so I can't demo the solution.

I'm doing this for my own use. But I would be happy to clean it up and package it for a PR if there is general interest in it.