- a large hill to climb. Added declarative examples to all the

- a large hill to climb.  Added declarative examples to all the
"basic relationship" examples, cleaned up the examples and added
some more explicitness.  Also renamed "treenodes" to "nodes" and
added self-referential declarative example.
- Added info/examples on how to join tables directly when querying with
joined table inheritance.
-  Starting to talk about hybrids in the main mapper docs some more.
introducoed the idea that synonyms are on their way out.
- SQL expressions as mapped attributes also gets better verbiage,
alternative approaches to them, including hybrids.
- modernized the hybrid example.
- object_session() as a standalone function wasn't documented ?!