tweak phame blog template a bit for better Facebook integration

Summary: this makes it more sensical when you hit "share" from a bookmarklet or cut and paste a link into FB, basically by having post-specific data when sharing a post.

Test Plan: looked at generated HTML on my test blog

Reviewers: epriestley

Reviewed By: epriestley

CC: chad, aran, Korvin

Differential Revision: https://secure.phabricator.com/D4266