Added new attribute :attr:`_orm.ORMExecuteState.is_column_load` to indicate
that a :meth:`_orm.SessionEvents.do_orm_execute` handler that a particular
operation is a primary-key-directed column attribute load, such as from an
expiration or a deferred attribute, and that WHERE criteria or additional
loader options should not be added to the query.   This has been added to
the examples which illustrate the :func:`_orm.with_loader_criteria` option.

The :func:`_orm.with_loader_criteria` option has been modified so that it
will never apply its criteria to the SELECT statement for an ORM refresh
operation, such as that invoked by :meth:`_orm.Session.refresh` or whenever
an expired attribute is loaded.   These queries are only against the
primary key row of the object that is already present in memory so there
should not be additional criteria added.

Added doc caveats for using lambdas.

Added test coverage for most ORMExecuteState flags and fixed a few
basic access issues.

Change-Id: I6707e4cf0dc95cdfb8ce93e5ca22ead86074baa7
References: #5760
Fixes: #5761
Fixes: #5762

* major additions to 1.4 migration doc; removed additional
  verbosity regarding caching methodology and reorganized the
  doc to present itself more as a "what's changed" guide

* as we now have a path for asyncio, update that doc so that
  we aren't spreading obsolete information

* updates to the 2.0 migration guide with latest info, however
  this is still an architecture doc and not a migration guide
  yet, will need further rework.

* start really talking about 1.x vs. 2.0 style everywhere.  Querying
  is most of the docs so this is going to be a prominent
  theme, start getting it to fit in

* Add introductory documentation for ORM example sections as these
  are too sparse

* new documentation for do_orm_execute(), many separate sections,
  adding deprecation notes to before_compile() and similar

* new example suites to illustrate do_orm_execute(),
  with_loader_criteria()

* modernized horizontal sharding examples and added a separate
  example to distinguish between multiple databases and single
  database w/ multiple tables use case

* introducing DEEP ALCHEMY, will use zzzeeksphinx 1.1.6

* no name for the alchemist yet however the dragon's name
  is Flambé

Change-Id: Id6b5c03b1ce9ddb7b280f66792212a0ef0a1c541