Get the gdata spreadsheet feed.

def get_feed(self):
        """Get the gdata spreadsheet feed."""
        return self.client.GetListFeed(self.key, self.worksheet,
            visibility='private' if self.is_authed else 'public',
            # TODO always use projection='values' ? What does full give me?
            projection='full' if self.is_authed else 'values')