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/profile.rst b/Doc/library/profile.rst
index 87e2fbe..236324d 100644
--- a/Doc/library/profile.rst
+++ b/Doc/library/profile.rst
@@ -1,4 +1,3 @@
-
 .. _profile:
 
 ********************
@@ -10,6 +9,9 @@
 .. module:: profile
    :synopsis: Python source profiler.
 
+**Source code:** :source:`Lib/profile.py` and :source:`Lib/pstats.py`
+
+--------------
 
 .. _profiler-introduction: