There is no `notify()` method in SSDPServer

[GilDev]

The README contains this example to send a NOTIFY message:

>>> from ssdpy import SSDPServer
>>> server = SSDPServer("my-service-identifier")
>>> server.notify()

But there doesn’t seem to be any notify() method, so I added this to the “server.py” file for now:

def notify(self):
    data = create_notify_payload(host=self._broadcast_ip,
                                 nt=self.device_type,
                                 usn=self.usn
                                 max_age=self.max_age,
    )
    self.sock.sendto(data, self._address)

I haven’t done a pull request yet as I guess this function lacks some value checks, some parameters and maybe other things. Maybe I’ll try to make it safer later if noone does it before me. 🙂