Backport source links from 3.x.

Existing links have been updated to use the new reST role.  In some
files, I have also made cosmetic changes to the header.
diff --git a/Doc/library/sysconfig.rst b/Doc/library/sysconfig.rst
index 38aae0a..5ba6fa2 100644
--- a/Doc/library/sysconfig.rst
+++ b/Doc/library/sysconfig.rst
@@ -5,10 +5,15 @@
    :synopsis: Python's configuration information
 .. moduleauthor:: Tarek Ziade <tarek@ziade.org>
 .. sectionauthor:: Tarek Ziade <tarek@ziade.org>
-.. versionadded:: 2.7
 .. index::
    single: configuration information
 
+.. versionadded:: 2.7
+
+**Source code:** :source:`Lib/sysconfig.py`
+
+--------------
+
 The :mod:`sysconfig` module provides access to Python's configuration
 information like the list of installation paths and the configuration variables
 relevant for the current platform.