Add schema for muse-xml, tweak verse formatting, fix goof from last patch.

Add schema for muse-xml, tweak verse formatting, fix goof from last patch.

* AUTHORS: Note that Brad Collins authored examples/muse-rnc.

* README (examples): Mention that other files are here as well.

* examples/muse-rnc.el: New file that implements a RelaxNG Compact schema
  for use with muse-xml.el.

* muse-xml.el: Mention the newly-contributed schema from Brad, and that
  muse-xml is in experimental status.
  (muse-xml-markup-regexps): Correct table-munging regexp.
  (muse-xml-markup-strings): Surround each verse line with <line></line>.
  Empty lines are marked up as <line />.

* muse-html.el (muse-html-markup-strings, muse-xhtml-markup-strings):
  s/last-stanza-end/end-last-stanza-line/.

* muse-mode.el (muse-visit-link-default): Make the temporary file
  visiting work as expected.

* muse-publish.el (muse-publish-markup-verse): Make use of
  'begin-verse-line and 'begin-last-stanza-line.  Use
  'end-last-stanza-line instead of 'last-stanza-end.

* muse.texi (Verse): Be a bit more clever with our example.
git-archimport-id: mwolson@gnu.org--2005/muse--main--1.0--patch-217