Queryset mixins (#629)

* add enum field

* add decorator for asyncio

* fix enum typing, additional tests, add docs

* add more tests

* query-mixin

* use dict to replace ordereddict

Co-authored-by: collerek <collerek@gmail.com>

tests/test_utils/test_queryset_utils.py

@@ -2,8 +2,7 @@ import databases
 import sqlalchemy
 
 import ormar
-from ormar.models.mixins import ExcludableMixin
-from ormar.queryset.prefetch_query import sort_models
+from ormar.queryset.queries.prefetch_query import sort_models
 from ormar.queryset.utils import (
     subtract_dict,
     translate_list_to_dict,