Govspeak renderer

[nacnudus]

Add an output format to translate markdown into govspeak (an extension of markdown), for submitting to Whitehall Publisher for publication on GOV.UK.

Lots of people think this is what govdown already does, and it's what they need it to do.

@sebastian-fox has done some work on this with regex, and @foster999 has published it as govspeakr.

If we do this, it will mean a lot more :::{.something} syntax for each component of govspeak that doesn't have an equivalent in markdown. It will also require some components that aren't part of the Design System, e.g. the download symbol.

[nacnudus]

Using commonmark instead of pandoc might avoid problems people have installing a recent enough version of pandoc to use lua filters. Or any pandoc at all. It wraps cmark, which is the reference implementation in C of the commonmark standard, and apparently cmark is easy to extend.

ROpenSci discussion