Open Graph: save FB author URL from Publicize and use it in OG

FB author URL saved in new custom field, _publicize_facebook_user
Open Graph: use profile link instead of display name for og:author
Open Graph: use FB Profile data, not FB Page data for og:author
Open Graph: escape og:author URL
Merge pull request #364 from jeherve/og_author_from_publicize

Open Graph: save FB author URL from Publicize and use it as og:author