API Additions
* Add elements Paragraph (<p>), Preformatted (<pre>), Image (<img>),
Highlight (<b>), Strong (<strong>), Alternate (<i>), Emphasis (<em>),
and Small (<small>).
* Add float_html_attribute().
* Add remove_css_classes() method to elements.
API-Incompatible Changes
* Rename ShortElement to VoidElement to conform to the HTML 5 standard.