Implements date range filtering on ``created_at``

def get_queryset(self):
        """
        Implements date range filtering on ``created_at``
        """
        kwargs = {}
        if self.start_at:
            kwargs.update({'%s__gte' % self.date_field: self.start_at})
        return super(DateRangeMixin, self).get_queryset().filter(**kwargs)