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/aifc.rst b/Doc/library/aifc.rst
index 0bb1635..1265423 100644
--- a/Doc/library/aifc.rst
+++ b/Doc/library/aifc.rst
@@ -10,6 +10,10 @@
    single: AIFF
    single: AIFF-C
 
+**Source code:** :source:`Lib/aifc.py`
+
+--------------
+
 This module provides support for reading and writing AIFF and AIFF-C files.
 AIFF is Audio Interchange File Format, a format for storing digital audio
 samples in a file.  AIFF-C is a newer version of the format that includes the