Add WAI-ARIA roles to typical HTML5 elements

Because all browsers treat newly added elements to HTML5 as a anonymous div, they have no specific meaning to screenreaders (thank you Erik Eggert at Fronten United).
see http://www.w3.org/TR/wai-aria/roles
see https://github.com/yatil/accessifyhtml5.js/blob/master/accessifyhtml5.js
see http://drupal.org/node/1179668