Issue #18214: Improve finalization of Python modules to avoid setting their globals to None, in most cases.

Issue #15699: The readline module now uses PEP 3121-style module initialization, so as to reclaim allocated resources (Python callbacks) at shutdown.
Original patch by Robin Schreiber.

Feature and tests by ClClaudiu.Popa, I added the doc changes.

gcov is great.

CID 1058763

"coverage-report" creates an instrumented Python build, runs unit tests
and creates a HTML. The report can be updated with "make coverage-lcov".

Patch by Sijin Joseph.

testcleanup directive is new as of 1.1, and we are currently running
1.0.7.  But using testsetup works just as well, and avoids the
unknown directive error when building the docs.

'SHA1' instead of 'SHA'.
Add more tests for hashlib and hash object attributes

'SHA1' instead of 'SHA'.

With the exception of the 'as_string' call in the policy docs.
That one is a separate issue.

Note that when building the docs sphinx is complaining about
.. testcleanup:: being an invalid directive.  I don't know
why this is, as I'm following the sphinx docs...but fortunately
the action is to omit the text in the body, so the generated
documentation is correct.

With help from jkloth on IRC, so it will hopefully work
this time :)