update validation chapter.
Doc updates.
added example template project
add a load listener to db objects to prevent ModelBase subclasses from sneaking in.
Remove needless super() call. ModelBase will never have a ctor.
tweak the sqlalchemy example.
fix the multiprot pres url.
minor updates to docs and examples.
add support for db_type attribute in ModelBase.Attribute
add missing spatial types to Spyne => SQLAlchemy type mapping
move the docs for the old way of integrating with SQLAlchemy to its module docstring.
re-write the sqlalchemy chapter.
improve the hybrid document section in sqlalchemy chapter.
Minor tweaks to the SQLAlchemy chapter.