Reworked the "setinputsizes()" set of dialect hooks to be correctly
extensible for any arbirary DBAPI, by allowing dialects individual hooks
that may invoke cursor.setinputsizes() in the appropriate style for that
DBAPI.   In particular this is intended to support pyodbc's style of usage
which is fundamentally different from that of cx_Oracle.  Added support
for pyodbc.

Fixes: #5649
Change-Id: I9f1794f8368bf3663a286932cfe3992dae244a10

Reworked the proxy creation used by scoped_session() to be
based on fully copied code with augmented docstrings and
moved it into langhelpers.  asyncio session, engine,
connection can now take
advantage of it so that all non-async methods are availble.

Overall implementation of most important accessors / methods
on AsyncConnection, etc. , including awaitable versions
of invalidate, execution_options, etc.

In order to support an event dispatcher on the async
classes while still allowing them to hold __slots__,
make some adjustments to the event system to allow
that to be present, at least rudimentally.

Fixes: #5628
Change-Id: I5eb6929fc1e4fdac99e4b767dcfd49672d56e2b2

It's better, the majority of these changes look more readable to me.
also found some docstrings that had formatting / quoting issues.

Change-Id: I582a45fde3a5648b2f36bab96bad56881321899b

This WIP is part of the final push for 1.4's docs
to fully "2.0-ize" what we can, and have it all ready.

So far this includes a rewrite of the 2.0 migration,
set up for the 1.4 /2.0 docs style, and a total redesign
of the index page using a new flex layout in zzzeeksphinx.

It also reworks some of the API reference sections
to have more subheaders.   zzzeeksphinx is also enhanced
to provide automatic summaries for all api doc section.

Change-Id: I01d360cb9c8749520246b96ee6496143c6037918

As the test suite has widespread use of many patterns
that are deprecated, enable SQLALCHEMY_WARN_20 globally
for the test suite but then break the warnings filter
out into a whole list of all the individual warnings
we are looking for.  this way individual changesets
can target a specific class of warning, as many of these
warnings will indivdidually affect dozens of files
and potentially hundreds of lines of code.

Many warnings are also resolved here as this
patch started out that way.   From this point
forward there should be changesets that target a
subset of the warnings at a time.

For expediency, updates some migration 2.0 docs
for ORM as well.

Change-Id: I98b8defdf7c37b818b3824d02f7668e3f5f31c94

The docs here were completely out of date and referred
to behaviors that are no longer true, behaviors that are
deprecated, etc.   For the moment, take out all the verbiage
so that nothing incorrect is present.   New ORM documentation
will need to be constructed to support this statement.

Change-Id: I4782aebb6443ceb68752c3b52b574fd30658ebc9

The server_side_cursors engine-wide feature relies upon
regexp parsing of statements a well as general guessing as
to when the feature should be used.   This is not within the
2.0 way of doing things and should be removed.

Additionally, mariadbconnector defaults to unbuffered cursors;
add new cursor hooks so that mariadbconnector can specify
buffered or unbuffered cursors without too much difficulty.
This will also correctly default mariadbconnector to buffered
cursors which should repair the segfaults we've been getting.

Try to restore the assert_raises that was removed in
5b6dfc0c38bf1f01da4b8 to see if mariadbconnector segfaults
are resolved.

Change-Id: I77f1c972c742e40694972f578140bb0cac8c39eb

"Implicit autocommit", which is the COMMIT that occurs when a DML or DDL
statement is emitted on a connection, is deprecated and won't be part of
SQLAlchemy 2.0.   A 2.0-style warning is emitted when autocommit takes
effect, so that the calling code may be adjusted to use an explicit
transaction.

As part of this change, DDL methods such as
:meth:`_schema.MetaData.create_all` when used against a
:class:`_engine.Engine` or :class:`_engine.Connection` will run the
operation in a BEGIN block if one is not started already.

The MySQL and MariaDB dialects now query from the information_schema.tables
system view in order to determine if a particular table exists or not.
Previously, the "DESCRIBE" command was used with an exception catch to
detect non-existent,  which would have the undesirable effect of emitting a
ROLLBACK on the connection. There appeared to be legacy encoding issues
which prevented the use of "SHOW TABLES", for this, but as MySQL support is
now at 5.0.2  or above due to :ticket:`4189`, the information_schema tables
are now available in all cases.

Fixes: #4846
Change-Id: I733a7e0e17477a63607fb9931c87c393bbd7ac57

it's not really correct that URL is mutable and doesn't do
any argument checking.   propose replacing it with an immutable
named tuple with rich copy-and-mutate methods.

At the moment this makes a hard change to the CreateEnginePlugin
docs that previously recommended url.query.pop().  I can't find
any plugins on github other than my own that are using this
feature, so see if we can just make a hard change on this one.

Fixes: #5526
Change-Id: I28a0a471d80792fa8c28f4fa573d6352966a4a79