'Create the session factory used by :meth:`create_scoped_session`.
The factory **must** return an object that SQLAlchemy recognizes as a session,
or registering session events may raise an exception.
Valid factories include a :class:`~sqlalchemy.orm.session.Session`
class or a :class:`~sqlalchemy.orm.session.sessionmaker`.
The default implementation creates a ``sessionmaker`` for :class:`SignallingSession`.
:param options: dict of keyword arguments passed to session class'

def create_session(self, options):

    return orm.sessionmaker(class_=SignallingSession, db=self, **options)
