Adds a textfilter which adds a data-hover attribute with the value of the link-text to links.

So:
<a href="http://www.drupal.org">Link to Drupal</a>
Becomes:
<a data-hover="Link to Drupal" href="http://www.drupal.org">Link to Drupal</a>

This is useful if you want to make fancy CSS links as seen here for instance.