around for a long time
- association proxy now returns None for proxied scalar that is also None, rather
than raising AttributeError. [ticket:2810]

- fix the targeting of module names moved around by using custom handlers for "Bases", etc.

that ``discriminator_on_association.py`` makes use of single table
inheritance do the work with the "discriminator".  Also
added a true "generic foreign key" example, which works similarly
to other popular frameworks in that it uses an open-ended integer
to point to any other table, foregoing traditional referential
integrity.  While we don't recommend this pattern, information wants
to be free.  Also in 0.8.3.

- Added a convenience class decorator :func:`.as_declarative`, is
a wrapper for :func:`.declarative_base` which allows an existing base
class to be applied using a nifty class-decorated approach.  Also
in 0.8.3.

associated with the ORM or its extensions can be retrieved.
This fulfills the common request of being able to inspect
all :class:`.QueryableAttribute` descriptors in addition to
extension types such as :class:`.hybrid_property` and
:class:`.AssociationProxy`.  See :attr:`.Mapper.all_orm_descriptors`.

:meth:`.MutableBase.coerce` method to be used, even though
the code seemed to indicate this intent, so this now works
and a brief example is added.  As a side-effect,
the mechanics of this event handler have been changed so that
new :class:`.MutableComposite` types no longer add per-type
global event handlers.  Also in 0.7.10

[ticket:2624]