Accept camelCase privacyStatus in Playlist#update

Previously only the underscored syntax :privacy_status was accepted.
We are better off accepting both forms, since one is more Ruby-style,
the other is what someone who knows the YouTube API expects.
Merge pull request #37 from Fullscreen/accept-camelcase-privacy-status

Accept camelCase privacyStatus in Playlist#update
Add content_owner.references to list References