Patch by Yury Selivanov.

Mostly documentation changes; the code changes are clarifications,
not semantic changes.

Issue #14837: SSL errors now have `library` and `reason` attributes describing precisely what happened and in which OpenSSL submodule.
The str() of a SSLError is also enhanced accordingly.

NOTE: this commit creates a reference leak.  The leak seems tied to the
use of PyType_FromSpec() to create the SSLError type.  The leak is on the
type object when it is instantiated:

>>> e = ssl.SSLError()
>>> sys.getrefcount(ssl.SSLError)
35
>>> e = ssl.SSLError()
>>> sys.getrefcount(ssl.SSLError)
36
>>> e = ssl.SSLError()
>>> sys.getrefcount(ssl.SSLError)
37

not contested, similar to what _thread.RLock already has.

timezone instance corresponding to the system local timezone when
called with no arguments.

timezone instance corresponding to the system local timezone when
called with no arguments.

for "parity" between PyArg_ParseTuple() and the Python/getargs.c static
function skipitem() for all possible "format units".

Add version  guard for Py_LIMITED_API additions.
Issue #15081: Document PyState_FindModule.
Patch by Robin Schreiber.

If an identical code line is in both at the end of if and else, it can as well
stand after the block. :) The code is from 464cf523485e, I didn't see it before
checking the commits in the web interface of course.

mktime() when timezone offest is supplied.

mktime() when timezone offest is supplied.

Original patch by Jim Jewett; see issue 14684.

These functions were originally added to support LZMA compression in the zipfile
module, and are not of interest for the majority of users.

They can be made public in 3.4 if there is user interest, but in the meanwhile,
I've opted to present a smaller, simpler API for the module's initial release.

Loosely based on the work by Hirokazu Yamamoto.