Added support for Canon printer (home-assistant-libs#183)

Example scan result:
2018-03-30 13:13:50.940639 - Found new service: canon_printer {'host':
'192.168.1.40', 'port': 80, 'ssdp_description':
'http:https://192.168.1.40:80/Canon_basic.xml', 'name': 'MX620 series
(UPnP)_4767DBFBCDEF', 'model_name': 'MX620 series', 'model_number':
'MX620 series', 'serial': 'D8492FFBCDEF', 'manufacturer': 'CANON INC.',
'udn': 'uuid:00000000-0000-1000-8000-D8492FFBCDEF'}

netdisco/discoverables/canon_printer.py

@@ -0,0 +1,13 @@
+"""Discover Canon Printers"""
+from . import SSDPDiscoverable
+
+
+class Discoverable(SSDPDiscoverable):
+ """Support for the discovery of Canon Printers"""
+
+ def get_entries(self):
+ """Get all the Canon Printer uPnP entries."""
+ return self.find_by_device_description({
+ "manufacturer": "CANON INC.",
+ "deviceType": "urn:schemas-cipa-jp:device:DPSPrinter:1"
+ })