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/modulefinder.rst b/Doc/library/modulefinder.rst
index a086206..40bf60f 100644
--- a/Doc/library/modulefinder.rst
+++ b/Doc/library/modulefinder.rst
@@ -1,16 +1,17 @@
-
 :mod:`modulefinder` --- Find modules used by a script
 =====================================================
 
+.. module:: modulefinder
+   :synopsis: Find modules used by a script.
 .. sectionauthor:: A.M. Kuchling <amk@amk.ca>
 
 
-.. module:: modulefinder
-   :synopsis: Find modules used by a script.
-
-
 .. versionadded:: 2.3
 
+**Source code:** :source:`Lib/modulefinder.py`
+
+--------------
+
 This module provides a :class:`ModuleFinder` class that can be used to determine
 the set of modules imported by a script. ``modulefinder.py`` can also be run as
 a script, giving the filename of a Python script as its argument, after which a