example, where the subclasses of AddressAssociation were not being
mapped as "single table inheritance", leading to problems when trying
to use the mappings further.

to allow ad-hoc display of the source of any file, as well as a "directory listing" structure.
- reorganize examples/ to take advantage of new extension.  in particular, keep moving all
the descriptive text for files etc. into module docstrings, taking more advantage of
self-documentation.

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.

- went through examples/ and cleaned out excess list() calls

examples and replaced with an updated set of
examples that use declarative mixins,
"generic_associations".   Each presents an alternative
table layout.