Add MP3 Player example (thanks Frank B)

examples/MP3Player/MP3Player.ino

+// Simple MP3 file player example
+//
+// Requires the prop-shield and Teensy 3.2 or 3.1
+// This example code is in the public domain.
+
+#include <Audio.h>
+#include <Wire.h>
+#include <SPI.h>
+#include <SerialFlash.h>
+#include <play_sd_mp3.h> // https://github.com/FrankBoesing/Arduino-Teensy-Codec-lib
+//#include <play_sd_aac.h>
+
+
+// GUItool: begin automatically generated code
+//AudioPlaySdWav           playSdWav1;     //xy=154,422
+AudioPlaySdMp3           playMp31; //xy=154,422
+AudioMixer4              mixer1;         //xy=327,432
+AudioOutputAnalog        dac1;           //xy=502,412
+AudioConnection          patchCord1(playMp31, 0, mixer1, 0);
+AudioConnection          patchCord2(playMp31, 1, mixer1, 1);
+AudioConnection          patchCord3(mixer1, dac1);
+// GUItool: end automatically generated code
+
+
+#define PROP_AMP_ENABLE    5
+#define FLASH_CHIP_SELECT  6
+
+void setup() {
+  AudioMemory(8); //4
+  delay(2000);
+
+  // Start SerialFlash
+  if (!SerialFlash.begin(FLASH_CHIP_SELECT)) {
+    while (1) {
+      Serial.println ("Cannot access SPI Flash chip");
+      delay (1000);
+    }
+  }
+
+  //Start Amplifier
+  pinMode(PROP_AMP_ENABLE, OUTPUT);
+  digitalWrite(PROP_AMP_ENABLE, HIGH);    // Enable Amplifier
+}
+
+void playFile(const char *filename)
+{
+
+  SerialFlashFile ff = SerialFlash.open(filename);
+  Serial.print("Playing file: ");
+  Serial.println(filename);
+
+  uint32_t sz = ff.size();
+  uint32_t pos = ff.getFlashAddress();
+
+  // Start playing the file.  This sketch continues to
+  // run while the file plays.
+  playMp31.play(pos,sz);
+
+  // Simply wait for the file to finish playing.
+  while (playMp31.isPlaying()) {}
+}
+
+
+void loop() {
+  playFile("rain.mp3");
+  delay(1000);
+}