Monkey patches for outstanding issues logged in the simple-rss project.

  * Add support for issued time field:
    http://rubyforge.org/tracker/index.php?func=detail&aid=13980&group_id=893&atid=3517
  * The '+' symbol is lost when escaping fields.
    http://rubyforge.org/tracker/index.php?func=detail&aid=10852&group_id=893&atid=3517