CLEAN access to 4ip extension former page/milestone

doc/sphinx/4ip_extension.rst

+HTTP 301: Page Moved Permanently
+================================
+
+This does no longer exists. Either you were looking for :ref:`ms33` or for the
+general :ref:`4ip_toc`

doc/sphinx/index.rst

@@ -3,6 +3,8 @@
    You can adapt this file completely to your liking, but it should at least
    contain the root `toctree` directive.
 
+.. _4ip_toc:
+
 Welcome to 4IP-extension documentation!
 =======================================