Change-Id: I7649576bd1e100fd6f8968f0256b074263943a44

The ORM Declarative system is now unified into the ORM itself, with new
import spaces under ``sqlalchemy.orm`` and new kinds of mappings.  Support
for decorator-based mappings without using a base class, support for
classical style-mapper() calls that have access to the declarative class
registry for relationships, and full integration of Declarative with 3rd
party class attribute systems like ``dataclasses`` and ``attrs`` is now
supported.

Fixes: #5508
Change-Id: I130b2b6edff6450bfe8a3e6baa099ff04b5471ff

Users of numpy and pandas should refer to this section
where we will try to catalog the common issues that don't
really have an automatic solution.

Fixes: #5552
Change-Id: I02990e328616ccb21933ffda1167c52256bace07

The populate_existing() method is actually changing
to be an execution option, however it has almost no
mention in the narrative docs so add docs in terms of the
1.x version first, including that we mention you almost
definitely want to use this method if you are also using
with_for_update().

Fixes: #5572
Fixes: #4774
Change-Id: Ieca916400622c1ffc1ae81204132a02a0983594c

Fixes some remaining issues detailed at #5428.

Fixes: #5428
Change-Id: I942a64411766fc82f30791eee570747a218af77d

This change includes mainly that the bracketed use within
select() is moved to positional, and keyword arguments are
removed from calls to the select() function.  it does not
yet fully address other issues such as keyword arguments passed
to the table.select().

Additionally, allows False / None to both be considered
as "disable" for all of select.correlate(), select.correlate_except(),
query.correlate(), which establishes consistency with
passing of ``False`` for the legact select(correlate=False)
argument.

Change-Id: Ie6c6e6abfbd3d75d4c8de504c0cf0159e6999108

Added support for PostgreSQL "readonly" and "deferrable" flags for all of
psycopg2, asyncpg and pg8000 dialects.   This takes advantage of a newly
generalized version of the "isolation level" API to support other kinds of
session attributes set via execution options that are reliably reset
when connections are returned to the connection pool.

Fixes: #5549
Change-Id: I0ad6d7a095e49d331618274c40ce75c76afdc7dd

The isolation level section in the docs inadvertently
copied the PostgreSQL example using the PGDialect.isolation_level
parameter and not the execution_options.  ensure only
the execution_options version is documented.

Change-Id: I94e02ede62d3dded40e3fcbce8d04608dc063108