Doc-generator combined description contains escaped HTML tags

[jautor]

With the addition of the "combined short and long description" support for normative document output, the combination of those descriptions occurs in doc_formatter, which means the combined description is carried through to all output formats.

This works fine for markdown, as the included HTML "list" tags survive processing, but for HTML output, the description text is processed with the HTML tags escaped, so they show up as text values in the resulting output.

Suggest that the building of the description output, which is already mostly processed in the html_formatter and markdown_formatter, be moved to those output processing routines. This may also affect CSV output (but I haven't looked to see if the description combination is even applicable to that output).