Make Ikiwiki directives work, and make Ikiwiki recognize Muse directives.

Make Ikiwiki directives work, and make Ikiwiki recognize Muse directives.

* examples/ikiwiki/IkiWiki/Plugin/muse.pm: Loop in Muse closer to the
  beginning of the publishing process, so that other HTML-producing
  Ikiwiki plugins can do their thing after we are done with the document.
  Otherwise, we would end up escaping their HTML.  Detect Muse-style
  directives.  Treat #tag, #tags, and #category directives like an
  Ikiwiki tag directive.  Treat every other directive as an Ikiwiki meta
  directive.

* lisp/muse-ikiwiki.el (muse-ikiwiki-markup-regexps)
  (muse-ikiwiki-markup-directive): Pass through Ikiwiki directives during
  publishing without modifying them.