Adds a subscriber to a subscriber list.

def add(self, list_id, email_address, name, custom_fields, resubscribe, consent_to_track, restart_subscription_based_autoresponders=False):
        """Adds a subscriber to a subscriber list."""
        validate_consent_to_track(consent_to_track)
        body = {
            "EmailAddress": email_address,
            "Name": name,
            "CustomFields": custom_fields,
            "Resubscribe": resubscribe,
            "ConsentToTrack": consent_to_track,
            "RestartSubscriptionBasedAutoresponders": restart_subscription_based_autoresponders}
        response = self._post("/subscribers/%s.json" %
                              list_id, json.dumps(body))
        return json_to_py(response)