Add 'The Python 2.3 Method Resolution Order' (#116435)

Author: hugovk

Doc/glossary.rst

@@ -800,8 +800,7 @@ Glossary
 
    method resolution order
       Method Resolution Order is the order in which base classes are searched
-      for a member during lookup. See `The Python 2.3 Method Resolution Order
-      <https://www.python.org/download/releases/2.3/mro/>`_ for details of the
+      for a member during lookup. See :ref:`python_2.3_mro` for details of the
       algorithm used by the Python interpreter since the 2.3 release.
 
    module

Doc/howto/index.rst

@@ -33,4 +33,5 @@ Currently, the HOWTOs are:
    annotations.rst
    isolating-extensions.rst
    timerfd.rst
+   mro.rst