deleteMessages method
Delete some or all messages in a topic
Implementation
Future deleteMessages(String topicName, List<DelRange> ranges, bool hard) {
var packet = _packetGenerator.generate(packet_types.Del, topicName);
var data = packet.data as DelPacketData;
data.what = 'msg';
data.delseq = ranges;
data.hard = hard;
packet.data = data;
return _send(packet);
}