Mermaid support?

I was wondering if you've considered [Mermaid](https://mermaidjs.github.io) support in `documentation`. (It's a way to describe diagrams textually in markdown files that render nicely.) It seems like it'd be a great alternative to ASCII-art for quite a few documentation tasks.

An example:

```text
graph TD;
A-->B;
A-->C;
B-->D;
C-->D;
```

would turn in to