Allow absolute URLs for image

README.md

@@ -62,7 +62,6 @@ Additionally, the plugin will use the following values, if present in a post's Y
 * `author` - The author of the post, e.g., "Dr. Jekyll". If none is given, feed readers will look to the feed author as defined in `_config.yml`. Like the feed author, this can also be an object.
 
 * `image` - URL of an image that is representative of the post.  
-  **Note:** URL must be relative to the site root, eg: `/images/example.png`
 
 ### Meta tags
 

lib/feed.xml

@@ -80,8 +80,12 @@
         <summary>{{ post.excerpt | strip_html | replace: '\n', ' ' | strip | xml_escape }}</summary>
       {% endif %}
 
-      {% if post.image %}
-        <media:thumbnail xmlns:media="http://search.yahoo.com/mrss/" url="{{ post.image | prepend: url_base | xml_escape }}" />
+      {% assign post_image = post.image %}
+      {% if post_image %}
+        {% unless post_image contains "://" %}
+          {% assign post_image = post_image | prepend: url_base | xml_escape  %}
+        {% endunless %}
+        <media:thumbnail xmlns:media="http://search.yahoo.com/mrss/" url="{{ post_image }}" />
       {% endif %}
     </entry>
   {% endunless %}

spec/fixtures/_posts/2014-03-02-march-the-second.md

@@ -1,4 +1,5 @@
 ---
+image: "https://cdn.example.org/absolute.png"
 ---
 
 March the second!

spec/jekyll-feed_spec.rb

@@ -89,6 +89,7 @@
 
   it "includes the item image" do
     expect(contents).to include('<media:thumbnail xmlns:media="http://search.yahoo.com/mrss/" url="http://example.org/image.png" />')
+    expect(contents).to include('<media:thumbnail xmlns:media="http://search.yahoo.com/mrss/" url="https://cdn.example.org/absolute.png" />')
   end
 
   context "parsing" do