we only have three uses at the moment, all of them in code blocks where
they could just as well (or maybe better) be comments. markdown can't do
callouts without another pandoc filter, so we'll turn them into comments
instead.
synapse would've benefited from inline links, but referencing an
external numbered list as plain text (instead of clickable links, like
callout lists had) seems even worse than putting urls into comments as
plain text.
markdown doesn't really have examples as a first-class construct. we'll
keep all examples that are referenced around for now, but all
unreferenced examples turn into invisible anchors. (turning them into
fourth-level headings in their files, as would be necessary for emacs,
removes them from the TOC anyway.)
productname, application, acronym, guilabel, and guibutton were so far
not rendered specially and can go away completely.
replaceable does render differently, but since it was only used twice
and in places where the intent should be clear without the extra markup
it can go as well.
makes sure that program listing tags are separated from their contents
by exactly a newline character. this makes the markdown translation
easier to verify (since no new newlines need to be inserted), and
there's no rendering difference anyway.
MD can only do the latter, so change them all over now to keeps diffs reviewable.
this also includes <literal><xref> -> <xref> where options are referenced since
the reference will implicitly add an inner literal tag.
markdown cannot represent those links. remove them all now instead of in
each chapter conversion to keep the diff for each chapter small and more
understandable.
matching on only `{...}` does not trigger if the role tag is preceded by
something usually considered a semantic separator that isn't a separator
as markdown knows it, e.g. punctuation characters.
