espat: implement MQTT subscribe functionality via blocking select/channels.

also refactor response processing for greater speed and efficiency.

Signed-off-by: Ron Evans <ron@hybridgroup.com>

espat/mqtt/token.go

@@ -0,0 +1,19 @@
+package mqtt
+
+import "time"
+
+type mqtttoken struct {
+	err error
+}
+
+func (t *mqtttoken) Wait() bool {
+	return true
+}
+
+func (t *mqtttoken) WaitTimeout(time.Duration) bool {
+	return true
+}
+
+func (t *mqtttoken) Error() error {
+	return t.err
+}