Handle embedded docbook footnotes and <literal> edge case.

Handle embedded docbook footnotes and <literal> edge case.

* lisp/muse-docbook.el: Implement more suggestions from Dale Smith.
 (muse-docbook-markup-strings): Use systemitem for example text.
 (muse-docbook-markup-paragraph): Allow for embedded footnotes that have
 <para></para> inside of them.

* lisp/muse-html.el (muse-html-escape-string): Don't deal with '&<>"'
  here at all.

* lisp/muse-publish.el (muse-publish-url-transforms): Add
  muse-publish-escape-specials-in-string to list by default.

* lisp/muse-publish.el (muse-publish-escape-specials): New optional third
  argument IGNORE-READ-ONLY determines whether or not to ignore the
  read-only property when transforming text.  Add docstring.
  (muse-publish-markup-word): Use non-nil third argument to
  muse-publish-escape-specials when we're publishing `='-delimited text.
  This allows =<literal><tag></literal>= to work as intended.

* lisp/muse-publish.el (muse-publish-escape-specials-in-string): Ignore
  arguments after the first so that we can include this in
  `muse-publish-url-transforms'.

* lisp/muse-publish.el (muse-publish-prepare-url): Add docstring.
git-archimport-id: mwolson@gnu.org--2005/muse--main--1.0--patch-158