Breaking change: Add disqus element.

Required adding disqusShortname = "XYZ" to config.toml
Details: http://gohugo.io/extras/comments/

This resolves #4.

layouts/posts/single.html

@@ -20,6 +20,9 @@
                 <br>
                 <p><a href="/posts/">Back to posts</a></p>
             </div>
+            <div class="disqus">
+                {{ template "_internal/disqus.html" . }}
+            </div>
         </div>
     </div>
 </div>