Add canonical link to all pages

views/other.erb

@@ -7,6 +7,7 @@
   <meta name="format-detection" content="telephone=no">
   <meta property="og:image" content="http://cdn.devdocs.io/images/icon-128.png">
   <title>DevDocs<%= ": #{@doc['name']} API Documentation" if doc_index_page? %></title>
+  <link rel="canonical" href="http://devdocs.io<%= request.path %>">
   <link rel="icon" type="image/x-icon" href="//cdn.devdocs.io/favicon.ico">
   <link rel="search" type="application/opensearchdescription+xml" href="/opensearch.xml" title="Search DevDocs">
   <link rel="stylesheet" href="<%= main_stylesheet_path %>" data-alt="<%= alternate_stylesheet_path %>">