Update references to Python docs in the sidebar index.

Patch contributed by Auke Willem Oosterhoff.

Doc/tools/sphinxext/indexsidebar.html

-            <h3>Download</h3>
-            <p><a href="{{ pathto('download') }}">Download these documents</a></p>
-	    <h3>Docs for other versions</h3>
-	    <ul>
-	      <li><a href="http://docs.python.org/2.7/">Python 2.7 (stable)</a></li>
-	      <li><a href="http://docs.python.org/3.3/">Python 3.3 (stable)</a></li>
-              <li><a href="http://www.python.org/doc/versions/">Old versions</a></li>
-            </ul>
+<h3>Download</h3>
+<p><a href="{{ pathto('download') }}">Download these documents</a></p>
+<h3>Docs for other versions</h3>
+<ul>
+  <li><a href="http://docs.python.org/2.7/">Python 2.7 (stable)</a></li>
+  <li><a href="http://docs.python.org/3.3/">Python 3.3 (stable)</a></li>
+  <li><a href="http://docs.python.org/3.5/">Python 3.5 (in development)</a></li>
+  <li><a href="http://www.python.org/doc/versions/">Old versions</a></li>
+</ul>
 
-            <h3>Other resources</h3>
-            <ul>
-              {# XXX: many of these should probably be merged in the main docs #}
-              <li><a href="http://www.python.org/dev/peps/">PEP Index</a></li>
-              <li><a href="http://wiki.python.org/moin/BeginnersGuide">Beginner's Guide</a></li>
-              <li><a href="http://wiki.python.org/moin/PythonBooks">Book List</a></li>
-              <li><a href="http://www.python.org/doc/av/">Audio/Visual Talks</a></li>
-            </ul>
+<h3>Other resources</h3>
+<ul>
+  {# XXX: many of these should probably be merged in the main docs #}
+  <li><a href="http://www.python.org/dev/peps/">PEP Index</a></li>
+  <li><a href="http://wiki.python.org/moin/BeginnersGuide">Beginner's Guide</a></li>
+  <li><a href="http://wiki.python.org/moin/PythonBooks">Book List</a></li>
+  <li><a href="http://www.python.org/doc/av/">Audio/Visual Talks</a></li>
+</ul>