update links to pdf and zipped docs to point to latest versions

content/doc/index.rst

@@ -14,9 +14,9 @@ Tutorial and reference manual
 -----------------------------
 
 * Browse online: `stable version </doc/1/>`_, `development version </doc/dev/>`_,
-* `download PDF <http://downloads.kwant-project.org/doc/kwant-doc-1.1.1.pdf>`_,
+* `download PDF <http://downloads.kwant-project.org/doc/latest.pdf>`_,
 * `download zipped HTML
-  <http://downloads.kwant-project.org/doc/kwant-doc-1.1.1.zip>`_ (for reading
+  <http://downloads.kwant-project.org/doc/latest.zip>`_ (for reading
   without web access).
 
 Interactive online course