List all tags in Muse's documentation.

List all tags in Muse's documentation.

* lisp/muse-publish.el (muse-publish-markup-region): Remove cruft that I
  was trying out.
  (muse-publish-contents-depth): New option that specifies the maximum
  depth of headings to include with <contents> tags.
  (muse-publish-contents-tag): Use it.
  (muse-publish-include-tag): Docfix.

* muse.texi (Paragraphs): Mention <center> and <quote> tags.
  (Tag Summary): New section that defines the syntax used for tags and
  gives a complete listing of all of the tags that Muse comes with, as
  well as some documentation for each tag.
  (HTML): Update documentation.
git-archimport-id: mwolson@gnu.org--2006/muse--main--1.0--patch-144