- logging scale-back; the echo_uow flag on Session is deprecated, and unit of work...

- logging scale-back; the echo_uow flag on Session is deprecated, and unit of work logging is now
class level like all the other logging.
- trimmed back the logging API, centralized class_logger() as the single point of configuration for
logging, removed per-instance logging checks from ORM.
- Engine and Pool logging remain at the instance level.  The modulus of "instance ids" has been upped
to 65535.  I'd like to remove the modulus altogether but I do see a couple of users each month
calling create_engine() on a per-request basis, an incorrect practice but I'd rather their applications
don't just run out of memory.