to rely upon server generated version identifiers, using triggers
or other database-provided versioning features, by passing the value
``False``.  The ORM will use RETURNING when available to immediately
load the new version identifier, else it will emit a second SELECT.
[ticket:2793]
- The ``eager_defaults`` flag of :class:`.Mapper` will now allow the
newly generated default values to be fetched using an inline
RETURNING clause, rather than a second SELECT statement, for backends
that support RETURNING.
- Added a new variant to :meth:`.ValuesBase.returning` called
:meth:`.ValuesBase.return_defaults`; this allows arbitrary columns
to be added to the RETURNING clause of the statement without interfering
with the compilers usual "implicit returning" feature, which is used to
efficiently fetch newly generated primary key values.  For supporting
backends, a dictionary of all fetched values is present at
:attr:`.ResultProxy.returned_defaults`.
- add a glossary entry for RETURNING
- add documentation for version id generation, [ticket:867]

with @_legacy_signature, will inspect incoming listener functions
to see if they match an older signature, will wrap into a newer sig
- add an event listen argument named=True, will send all args as
kw args so that event listeners can be written with **kw, any combination
of names
- add a doc system to events that writes out the various calling styles
for a given event, produces deprecation messages automatically.
a little concerned that it's a bit verbose but will look at it up
on RTD for awhile to get a feel.
- change the calling signature for bulk update/delete events - we have
the BulkUD object right there, and there's at least six or seven things
people might want to see, so just send the whole BulkUD in
[ticket:2775]

- begin consolidating docs for dialects to be more self contained
- add a separate section for "external" dialects
- not sure how we're going to go with this yet.