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/sunau.rst b/Doc/library/sunau.rst
index 3f231b4..4bdb99b 100644
--- a/Doc/library/sunau.rst
+++ b/Doc/library/sunau.rst
@@ -1,4 +1,3 @@
-
 :mod:`sunau` --- Read and write Sun AU files
 ============================================
 
@@ -6,6 +5,9 @@
    :synopsis: Provide an interface to the Sun AU sound format.
 .. sectionauthor:: Moshe Zadka <moshez@zadka.site.co.il>
 
+**Source code:** :source:`Lib/sunau.py`
+
+--------------
 
 The :mod:`sunau` module provides a convenient interface to the Sun AU sound
 format.  Note that this module is interface-compatible with the modules