- Structural memory use has been improved via much more significant use

- Structural memory use has been improved via much more significant use
of ``__slots__`` for many internal objects.  This optimization is
particularly geared towards the base memory size of large applications
that have lots of tables and columns, and greatly reduces memory
size for a variety of high-volume objects including event listening
internals, comparator objects and parts of the ORM attribute and
loader strategy system.