DOC: use pathto(master_doc) for active tab

Author: hagenw

doc/_template/layout.html

@@ -6,9 +6,9 @@
   {% include "searchbox.html" %}
 
 	<div class="rtd-nav">
-		<a href="http://sfstoolbox.org/">Theory</a>
-		<a href="http://matlab.sfstoolbox.org/">Matlab</a>
-		<a class="active" href="http://python.sfstoolbox.org/">Python</a>
+		<a href="http://sfstoolbox.org">Theory</a>
+		<a href="http://matlab.sfstoolbox.org">Matlab</a>
+		<a class="active" href="{{ pathto(master_doc) }}">Python</a>
 	</div> 
 
 {% endblock %}