Implemented the SQLAlchemy 2 :func:`.future.create_engine` function which
is used for forwards compatibility with SQLAlchemy 2.   This engine
features always-transactional behavior with autobegin.

Allow execution options per statement execution.  This includes
that the before_execute() and after_execute() events now accept
an additional dictionary with these options, empty if not
passed; a legacy event decorator is added for backwards compatibility
which now also emits a deprecation warning.

Add some basic tests for execution, transactions, and
the new result object.   Build out on a new testing fixture
that swaps in the future engine completely to start with.

Change-Id: I70e7338bb3f0ce22d2f702537d94bb249bd9fb0a
Fixes: #4644

The change in I5343a2d270ed5a8c654b9fe13dff40cdf54649ed
left the name "databases" present in one spot, which is usually
not reached unless tests are being run on only partial files
where not every dialect has been imported.

Change-Id: I5a8776b412eaf2476f8a93eebc31448b6f9218ee

The databases package is an old alias to the dialect package, and its usage
is now deprecated

Change-Id: I5343a2d270ed5a8c654b9fe13dff40cdf54649ed

This collection was added only for the benefit of unit tests
and is unnecessary for the pool to function.  As SQLAlchemy 2.0
will be removing the automatic handling of connections that are
garbage collection, remove this collection so that we ultimately
don't need a weakref handler to do anything within the pool.
The handler will do nothing other than emit a warning that
a connection was dereferenced without being explicitly returned
to the pool, invalidated, or detached.

Change-Id: I4ca196270d5714efbac44dbf6f034e8c7f0af58a

Removed all dialect code related to support for Jython and zxJDBC. Jython
has not been supported by SQLAlchemy for many years and it is not expected
that the current zxJDBC code is at all functional; for the moment it just
takes up space and adds confusion by showing up in documentation. At the
moment, it appears that Jython has achieved Python 2.7 support in its
releases but not Python 3.   If Jython were to be supported again, the form
it should take is against the Python 3 version of Jython, and the various
zxJDBC stubs for various backends should be implemented as a third party
dialect.

Additionally modernized logic that distinguishes between "cpython"
and "pypy" to instead look at platform.python_distribution() which
reliably tells us if we are cPython or not; all booleans which
previously checked for pypy and sometimes jython are now converted
to be "not cpython", this impacts the test suite for tests that are
cPython centric.

Fixes: #5094
Change-Id: I226cb55827f997daf6b4f4a755c18e7f4eb8d9ad

Change-Id: I08440dc25e40ea1ccea1778f6ee9e28a00808235

in trying to apply 2020 copyright to files, the pre-commit
hooks complain about random file issues.

- remove old corrections.py utility, this had something to do
  with repairing refs in the sphinx docs

- run pre commit hooks on all files

- formatting adjustments to work around code formatting collisions
  (long import lines that zimports can't rewrite correctly)

Change-Id: I260744866f69e902eb93665c7c728ee94d3371a2

The "threadlocal" execution strategy, deprecated in 1.3, has been
removed for 1.4, as well as the concept of "engine strategies" and the
``Engine.contextual_connect`` method.  The "strategy='mock'" keyword
argument is still accepted for now with a deprecation warning; use
:func:`.create_mock_engine` instead for this use case.

Fixes: #4632
Change-Id: I8a351f9fa1f7dfa2a56eec1cd2d1a4b9d65765a2
(cherry picked from commit b368c49b44c5716d93c7428ab22b6761c6ca7cf5)

A large change throughout the library has ensured that all objects, parameters,
and behaviors which have been noted as deprecated or legacy now emit
``DeprecationWarning`` warnings when invoked.   As the Python 3 interpreter now
defaults to displaying deprecation warnings, as well as that modern test suites
based on tools like tox and pytest tend to display deprecation warnings,
this change should make it easier to note what API features are obsolete.

See the notes added to the changelog and migration notes for further
details.

Fixes: #4393
Change-Id: If0ea11a1fc24f9a8029352eeadfc49a7a54c0a1b

Change-Id: I6a71f4924d046cf306961c58dffccf21e9c03911