We no longer wrap section headings in a `\hypertarget`.
This is unnecessary (hyperref creates an anchor based on the
label) and it interferes with tagging.
In addition, we now use `\hyperref` rather than `\hyperlink`
for internal links.
Currently `\hypertarget` is still being used for link anchors
not on headings.
Closes#8744. Thanks to @u-fischer.
If this is present on a heading with the 'unnumbered' class,
the heading won't appear in the TOC. This class has no
effect if 'unnumbered' is not also specified.
This affects HTML-based writers (including slide shows
and epub), LateX (including beamer), RTF, and PowerPoint.
Other writers do not yet support `unlisted`.
Closes#1762.
John MacFarlane