add exclude method on QuerySet and fix missing default values on creation

tests/test_models.py

@@ -165,6 +165,18 @@ async def test_model_filter():
             products = await Product.objects.all(name__icontains="T")
             assert len(products) == 2
 
+            products = await Product.objects.exclude(rating__gte=4).all()
+            assert len(products) == 1
+
+            products = await Product.objects.exclude(rating__gte=4, in_stock=True).all()
+            assert len(products) == 2
+
+            products = await Product.objects.exclude(in_stock=True).all()
+            assert len(products) == 1
+
+            products = await Product.objects.exclude(name__icontains="T").all()
+            assert len(products) == 1
+
             # Test escaping % character from icontains, contains, and iexact
             await Product.objects.create(name="100%-Cotton", rating=3)
             await Product.objects.create(name="Cotton-100%-Egyptian", rating=3)