How to support Markdown templating

[jackfranklin]

It's possible that some may not like Doccy's default Markdown for formatting, and we should make it possible to change this.

I'm envisaging some JSON file that looks something like:

{
  "param": "- `{{name}}` (`{{type}}`): {{description}",
}

But that might become unwieldy quickly...

[jackfranklin]

This way, Doccy's formatting could also be defined via these templates, which would be nice. Good to pull the formatting out of being hidden within the JS.

[jonathan-fielding]

I think this example works quite well, the unwieldily issue may never happen and could be addressed in v2 if we need to