Remove hgroup from theme. It's dead now: http://www.sitepoint.com/html5-hgroup-element-dropped/. In its place a div will be use that inherits the old class that was being applied to header.
Restore site-header class to header element and give site-branding class to title and description wrapper div. See #206.
Merge pull request #206 from Automattic/rip-hgroup

Remove hgroup from theme. It's dead now.