feat(protocol): job messages, protocol version and job model (#7)

internal/master/events/broker_test.go

@@ -46,3 +46,7 @@ func TestBroker_SlowSubscriberDoesNotBlockPublish(t *testing.T) {
 		t.Fatal("Publish blocked on a slow subscriber")
 	}
 }
+
+func TestJobTopic(t *testing.T) {
+	assert.Equal(t, Topic("job-42"), JobTopic(42))
+}