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/pydoc.rst b/Doc/library/pydoc.rst
index e5f8fe2..8343452 100644
--- a/Doc/library/pydoc.rst
+++ b/Doc/library/pydoc.rst
@@ -1,4 +1,3 @@
-
 :mod:`pydoc` --- Documentation generator and online help system
 ===============================================================
 
@@ -15,6 +14,10 @@
    single: documentation; online
    single: help; online
 
+**Source code:** :source:`Lib/pydoc.py`
+
+--------------
+
 The :mod:`pydoc` module automatically generates documentation from Python
 modules.  The documentation can be presented as pages of text on the console,
 served to a Web browser, or saved to HTML files.