Add markup for comments, via parts of patch-261.
* experimental/muse-xml.el (muse-xml-markup-strings): Produce markup for
'comment-begin and 'comment-end.
* lisp/muse-docbook.el (muse-docbook-markup-strings): Ditto.
* lisp/muse-html.el (muse-html-markup-strings): Ditto.
* lisp/muse-texinfo.el (muse-texinfo-markup-strings): Ditto.
* lisp/muse-latex.el (muse-latex-markup-strings): Ditto.
* lisp/muse-publish.el (muse-publish-comments-p): New option that
determines whether comments should be deleted or published. Default is
to delete.
(muse-publish-markup-comment, muse-publish-comment-tag): Use
muse-publish-comments-p.
git-archimport-id: mwolson@gnu.org--2005/muse--rel--3.02--patch-4