Add heos discoverable (#250)

Author: andrewsayre

netdisco/discoverables/heos.py

@@ -0,0 +1,10 @@
+"""Discover Heos devices."""
+from . import SSDPDiscoverable
+
+
+class Discoverable(SSDPDiscoverable):
+    """Add support for discovering DLNA services."""
+
+    def get_entries(self):
+        """Get all the HEOS devices."""
+        return self.find_by_st("urn:schemas-denon-com:device:ACT-Denon:1")