code: static String unescape(String input)
      {
          if (input.isEmpty())
              return input;
  
          String res = input.replaceAll("\\\\:", ":");
          char last = res.charAt(res.length() - 1);
          return last == '!' ? res.substring(0, res.length() - 1) : res;
      }
docs: /*
  Reverses the effect of espace().
  Replaces all occurences of "\:" by ":" and remove last character if it is '!'.