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/inspect.rst b/Doc/library/inspect.rst
index 850ff08..e05618e 100644
--- a/Doc/library/inspect.rst
+++ b/Doc/library/inspect.rst
@@ -1,4 +1,3 @@
-
 :mod:`inspect` --- Inspect live objects
 =======================================
 
@@ -10,6 +9,10 @@
 
 .. versionadded:: 2.1
 
+**Source code:** :source:`Lib/inspect.py`
+
+--------------
+
 The :mod:`inspect` module provides several useful functions to help get
 information about live objects such as modules, classes, methods, functions,
 tracebacks, frame objects, and code objects.  For example, it can help you