Add markup for non-breaking space.
* lisp/muse-docbook.el (muse-docbook-markup-strings): Add markup string
for 'no-break-space.
* lisp/muse-groff.el (muse-groff-markup-strings): Ditto.
* lisp/muse-html.el (muse-html-markup-strings): Ditto.
* lisp/muse-latex.el (muse-latex-markup-strings): Ditto.
* lisp/muse-texinfo.el (muse-texinfo-markup-strings): Ditto.
* lisp/muse-xml.el (muse-xml-markup-strings): Ditto.
* lisp/muse-publish.el (muse-publish-markup-regexps)
(muse-publish-markup-functions): Interpret "~~" as a non-breaking
space. Thanks to Ken Brown for the suggestion.
(muse-publish-markup-no-break-space): New function that publishes a
non-breaking space.
git-archimport-id: mwolson@gnu.org--2005/muse--main--1.0--patch-323