Commands, to:

     - Play MP3              MQTT topic: "/mrdiynotifier/play"
                             MQTT load: http://url-to-the-mp3-file/file.mp3

     - Play Icecast Stream   MQTT topic: "/mrdiynotifier/stream"
                             MQTT load: http://url-to-the-icecast-stream/file.mp3

     - Play Ringtone         MQTT topic: "/mrdiynotifier/tone"
                              MQTT load: RTTTL formated text, example: Soap:d=8,o=5,b=125:g,a,c6,p,a,4c6,4p,a,g,e,c,4p,4g,a

     - Say Text              MQTT topic: "/mrdiynotifier/say"
                              MQTT load: Text to be read, example: Hello There. How. Are. You?

     - Change Volume         MQTT topic: "/mrdiynotifier/volume"
                              MQTT load: a double between 0.00 and 1.00, example: 0.7

     To get status:

     - The notifier sends status update on this MQTT topic: "/mrdiynotifier/status"

                  "playing"       either paying an mp3, streaming, playing a ringtone or saying a text
                  "idle"          waiting for a command
                  "error"         error when receiving a command: example: MP3 file URL can't be loaded
                  "connected"     device just connected to MQTT server

     - The notifier plays a 2 second audio clip when it is first booted and connected to Wifi