Try to fix some issues with <markup> in headers and footers

Try to fix some issues with <markup> in headers and footers

* lisp/muse-publish.el (muse-markup-tag-info): Make into a function.
  Move common code here, rather than duplicating it in two places.  Deal
  with case where muse-publish-use-header-footer-tags is non-nil.
  (muse-publish-markup-specials, muse-publish-inhibit-style-hooks)
  (muse-inhibit-style-tags): Move higher to avoid byte-compiler warning.
  (muse-publish-use-header-footer-tags): New variable that indicates
  whether we should use just the header and footer tags, rather than the
  full set.
  (muse-insert-file-or-string): Bind muse-publish-use-header-footer-tags
  to t.
  (muse-publish-markup-tag, muse-publish-call-tag-on-buffer): Simplify
  call to muse-markup-tag-info.
  (muse-publish-mark-up-tag): Bind muse-publish-use-header-footer-tags to
  nil.
git-archimport-id: mwolson@gnu.org--2006/muse--main--1.0--patch-395