- write a better XSL stylesheet? I am not an XSL expert.
- evaluate the use of the <ttl/> RSS element.
- use the <enclosure/> element for pump.io media objects
- use the <enclosure/> element for images on dilbert.com
- show cards directly in RSS items for twitter.com
- check the encoding of the tweets when UTF is used,
  maybe solvable with mb_convert_encoding()?
  See http://php.net/manual/en/domdocument.loadhtml.php