Make escaping of brackets in links work properly.

Make escaping of brackets in links work properly.

* lisp/muse-colors.el (muse-colors-explicit-link): If the link has
  escaped characters, display them unescaped.

* lisp/muse-mode.el (muse-make-link): Handle case where we are given no
  link.
  (muse-edit-link-at-point): Unescape the link before presenting it to
  the user for editing.

* lisp/muse-publish.el (muse-publish-escape-specials-in-string): Minor
  coding style fix.
  (muse-publish-url): Unescape the link description before doing further
  transforms on it.  The link has already been unescaped.

* lisp/muse.el (muse-sort-by-rating): Minor coding style fix.
  (muse-escape-specials-in-string): New function that escapes specials in
  a string.  This differs from Muse's other specials-escaping routines in
  that it replaces strings rather than characters, and is reversible if
  the specials are defined properly.
  (muse-replace-regexp-in-string): Docfix.
  (muse-link-specials): New variable containing the specials that Muse
  uses to handle syntactic issues with link text.  Namely: brackets.  The
  percent sign must also be escaped since it is used in the escaped text.
  (muse-link-escape, muse-link-unescape): Call
  muse-escape-specials-in-string.  Embarrassingly, these functions
  previously had no effect before.
git-archimport-id: mwolson@gnu.org--2006/muse--main--1.0--patch-164