Add a few missing source links from 2.7 and harmonize lib docs headers
diff --git a/Doc/library/atexit.rst b/Doc/library/atexit.rst
index 5b87b94..f2dccc2 100644
--- a/Doc/library/atexit.rst
+++ b/Doc/library/atexit.rst
@@ -6,6 +6,9 @@
.. moduleauthor:: Skip Montanaro <skip@pobox.com>
.. sectionauthor:: Skip Montanaro <skip@pobox.com>
+**Source code:** :source:`Lib/atexit.py`
+
+--------------
The :mod:`atexit` module defines functions to register and unregister cleanup
functions. Functions thus registered are automatically executed upon normal