Add Open Graph meta tags

app/views/asciicasts/_discovery_tags.html.erb

@@ -0,0 +1,11 @@
+<!-- oEmbed -->
+<link rel="alternate" type="application/json+oembed" href="<%= page.asciicast_oembed_url(:json) %>" />
+<link rel="alternate" type="text/xml+oembed" href="<%= page.asciicast_oembed_url(:xml) %>" />
+
+<!-- Open Graph -->
+<meta property="og:title" content="<%= page.asciicast_title %>" />
+<meta property="og:type" content="website" />
+<meta property="og:url" content="<%= asciicast_url(page.asciicast) %>" />
+<meta property="og:image" content="<%= asciicast_url(page.asciicast, format: :png) %>" />
+<meta property="og:description" content="<%= page.description %>" />
+<meta property="og:site_name" content="asciinema.org" />

app/views/asciicasts/show.html.slim

@@ -1,7 +1,6 @@
 - content_for(:title, page.title)
 - content_for(:head) do
-  link rel="alternate" type="application/json+oembed" href="#{page.asciicast_oembed_url(:json)}"
-  link rel="alternate" type="text/xml+oembed" href="#{page.asciicast_oembed_url(:xml)}"
+  = render 'discovery_tags', page: page
 
 .asciicast-page
   section.cinema