[Feature Request] Switch to using markdown-it-diagrams for mermaid support, get svgbob for free

[dmayle]

Hi!

This is a feature request to switch to using markdown-it-diagrams for mermaidjs support, because it also includes a WASM-compiled version of svgbob which would allow for ascii diagrams without an external server.

https://github.com/agoose77/markdown-it-diagrams