feat(isListening): add isListening func to see if it is actively listening

Author: asas1asas200

src/rdm6300.cpp

@@ -122,3 +122,8 @@ void Rdm6300::listen(void)
 {
 	_serial->listen();
 }
+
+bool Rdm6300::isListening(void)
+{
+	return _serial->isListening();
+}

src/rdm6300.h

@@ -41,6 +41,7 @@ class Rdm6300
 		uint32_t get_tag_id(void);
 		bool is_tag_near(void);
 		void listen(void);
+		bool isListening(void);
 	private:
 #ifdef RDM6300_HARDWARE_SERIAL
 		HardwareSerial *_hardware_serial = NULL;