2.3.0

Changes:

• Fix client query_and_return return type.

  Client has no knowledge of what the return type is or should be. Fixed
  to return RealDictRow & removed the T TypeVar from sync_client.

• Fix CRUD method return types.

  Previously, the built-in methods on the CRUD objects were returning the
  raw data from the Client's execute_and_return() method, of type
  RealDictRow from psycopg2.extras. Now each CRUD object also requires
  a return type object of type Type[T] to be passed as a second argument
  on initialization, which is then used to initialize a return type object
  from the db query results (i.e. an instance of ModelData) to be
  returned.

• Also generalizes model.base.ensure_exactly_one() to accept any list
  object.