Add support for django serializers

[travfu]

Can support for django.core.serializers.serialize be added? see django doc on subject.

Currently, strategy field's value_to_string will return a stringified class instance '<path.to.Strategy object at 0xffff89fd9190>', when I imagine we would want it to be something like "path.to.Strategy"

Proposal
since StrategyField is a CharField, something like this should work

class AbstractStrategyField(models.Field):
    def value_to_string(self, obj):
        value = self.value_from_object(obj)
        return self.get_prep_value(value)