feature request: support mermaid charts

[qun-huang]

Hello,

Would it be possible to support rendering of mermaid charts?

https://github.com/mermaid-js/mermaid

Thanks!

[IAmKongHai]

+1

[OiCkilL]

+2

[yumedzi]

+3

[SethCalkins]

I opened a PR for this --- it's fully tested and working on my end #172