add facebook opengraph tags

_includes/head.html

@@ -6,7 +6,7 @@
   <title>{% if page.title %}{{ page.title }}{% else %}{{ site.title }}{% endif %}</title>
 
   <meta name="author" content="{{ site.author.name }}" />
-  <meta name="description" content="{{ site.description }}">
+  <meta name="description" content="{% if page.subtitle %}{{ page.subtitle }}{% else %}{{ site.description }}{% endif %}">
 
   <link rel="alternate" type="application/rss+xml" title="{{ site.title }} - {{ site.description }}" href="{{ site.baseurl }}/feed.xml" />
 
@@ -45,4 +45,23 @@
 	  <link rel="stylesheet" href="//fonts.googleapis.com/css?family={{ font }}" />
     {% endfor %}
   {% endif %}
+  
+  <!-- Facebook OpenGraph tags -->
+  <meta property="og:title" content="{% if page.title %}{{ page.title }}{% else %}{{ site.title }}{% endif %}" />
+  <meta property="og:type" content="website" />
+  
+  {% if page.id %}
+  <meta property="og:url" content="{{ site.url }}{{ page.url }}/" />
+  {% else %}
+  <meta property="og:url" content="{{ site.url }}{{ page.url | remove: '/index.html' | remove: '.html' }}" />
+  {% endif %}
+  
+  {% if page.fb-img %}
+  <meta property="og:image" content="{{ page.fb-img }}" />
+  {% elif site.avatar %}
+  <meta property="og:image" content="{{ site.url }}{{ site.avatar }}" />
+  {% else %}
+  <meta property="og:image" content="" />
+  {% endif %}
+  
 </head>