Move JSONValue directive from BODS into our contrib library

[timgdavies]

For BODS I created a directive to display any string fragment of a JSON document.

This is currently in bods conf.py here and probably should become part of this repo longer term.

[jpmckinney]

Now here: https://github.com/openownership/data-standard/blob/8c9356c54b1a856b291b75cf980b6eecbef58787/docs/conf.py#L190-L214