The intention is to convert --config-help and --long-help outputs to
DocBook XML and XHTML rather than AsciiDoc, so that the converter does
not have to work around the intricate AsciiDoc syntax. However, this
commit does not yet connect the script to doc/Makefile.
XHTML could be generated from DocBook XML, but the script outputs it
directly because our DocBook is primarily intended for manual pages
and so does not have all the links that are useful in HTML.
