automatic reflection support for the "secondary" table referred
to by a :func:`.relationship`.   "secondary", when specified
either as a string table name, or as a :class:`.Table` object with
only a name and :class:`.MetaData` object will also be included
in the reflection process when :meth:`.DeferredReflection.prepare`
is called. [ticket:2865]
- clsregistry._resolver() now uses a stateful _class_resolver()
class in order to handle the work of mapping strings to
objects.   This is to provide for simpler extensibility, namely
a ._resolvers collection of ad-hoc name resolution functions;
the DeferredReflection class adds its own resolver here in order
to handle relationship(secondary) names which generate new
Table objects.

as the string name of a class or other argument within
declarative using :func:`.relationship`.

More fixes for cross references and reducing warnings (3rd wave)

correctly with table or column names that contain non-ASCII
characters. [ticket:2869]

We should probably reword this entirely as, IMHO, this should be in the
changelog and not in the doc proper (which should only describe the
current state of affairs).