Use ronn-ng to generate the documentation

[spacewander]

Currently we are using ronn to convert markdown docs to man pages and html files. Ronn is not longer maintained so we want to use ronn-ng instead.

There are two blocking issues about ronn-ng:

• https://github.com/apjanke/ronn-ng/issues/44
• https://github.com/apjanke/ronn-ng/issues/45

[thoward27]

I'd also suggest pandoc for consideration.

[elonderin]

and i propose asciidoc b/c it has a defined syntax