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'.