Support for rendering mermaid md

[LeskoIam]

It would be really great if rendering of mermaid markdown could be added?

[redimp]

I think adding mermaid rendering would be a useful feature.

A mermaid block like this

```mermaid
graph TD;
    A-->B;

would be rendered when viewing the page. Is that what you have in mind?

[LeskoIam]

Exactly. A code block, just like gihub supports it.

flowchart
    NO_MM(["No mermaid support"])
    MM(["Mermaid supported"])
    NO_MM -- mermaid markdown is awesome --> MM

[redimp]

Released in 2.6.0.