Function open_graph 

pub fn open_graph(
    page_title: &str,
    description: &str,
    image: &str,
    url: &str,
    og_type: &str,
    site_name: Option<&str>,
) -> Vec<Element>

Open Graph tags for a page.

Emits og:title, og:description, og:image, og:url, og:type and, when supplied, og:site_name — in that order.