FIX: add API to top banner

Author: jklymak

doc/_templates/layout.html

@@ -56,6 +56,7 @@
         <ul>
             <li><a href="{{ pathto('users/installing') }}">Installation</a></li>
             <li><a href="{{ pathto('contents') }}">Documentation</a></li>
+            <li><a href="{{ pathto('api/index') }}">API</a></li>
             <li><a href="{{ pathto('gallery/index') }}">Examples</a></li>
             <li><a href="{{ pathto('tutorials/index') }}">Tutorials</a></li>
             <li><a href="{{ pathto('devel/index') }}">Contributing</a></li>