Add mDNS server to advertise the device to ZHA

[sarg]

Implements #9. I've compiled it if you want to try: mdns.gz

By default it advertises tuya-local hostname and the service name is _zigbee-ezsp._tcp. These could be changed as /tuya/mdns --service _my-service._tcp._local --hostname my-hostname Upload to /tuya/mdns and add to the startup script:

echo "/tuya/mdns &" >> /tuya/tuya_start.sh