Add missing attributes to sqlalchemy.orm (#126)

Author: kasium

sqlalchemy-stubs/orm/__init__.pyi

@@ -3,6 +3,8 @@ from typing import Mapping
 from typing import Optional
 from typing import Tuple
 
+from . import exc
+from . import mapper as mapperlib
 from . import strategy_options
 from .attributes import AttributeEvent as AttributeEvent
 from .attributes import InstrumentedAttribute as InstrumentedAttribute