add getCodec() and getCodecname() functions

getCodecname() allows for simple display of the used codec,
getCodec() together with the exported enum of codec values allows for
user defined codec names like this stupid example:
  switch (audio.getCodec()) {
    case Audio::CODEC_M4A:
    case Audio::CODEC_AAC:
      Serial.println("AAC codec!");
      break;
    case Audio::CODEC_FLAC:
    case AUDIO::CODEC_OGG_FLAC:
      Serial.println("FLAC!");
      break;
  }

src/Audio.h

@@ -193,6 +193,10 @@ public:
     void setTone(int8_t gainLowPass, int8_t gainBandPass, int8_t gainHighPass);
     [[deprecated]]void setInternalDAC(bool internalDAC = true, i2s_dac_mode_t channelEnabled = I2S_DAC_CHANNEL_LEFT_EN);
     void setI2SCommFMT_LSB(bool commFMT);
+    int getCodec() {return m_codec;}
+    const char *getCodecname() {return codecname[m_codec];}
+    enum : int { CODEC_NONE, CODEC_WAV, CODEC_MP3, CODEC_AAC, CODEC_M4A, CODEC_FLAC, CODEC_OGG,
+                 CODEC_OGG_FLAC, CODEC_OGG_OPUS};
 
 private:
     void UTF8toASCII(char* str);
@@ -365,12 +369,10 @@ private:
         return expectedLen;
     }
 
-
 private:
+    const char *codecname[9] = {"unknown", "WAV", "MP3", "AAC", "M4A", "FLAC", "OGG", "OGG FLAC", "OPUS"};
     enum : int { APLL_AUTO = -1, APLL_ENABLE = 1, APLL_DISABLE = 0 };
     enum : int { EXTERNAL_I2S = 0, INTERNAL_DAC = 1, INTERNAL_PDM = 2 };
-    enum : int { CODEC_NONE, CODEC_WAV, CODEC_MP3, CODEC_AAC, CODEC_M4A, CODEC_FLAC, CODEC_OGG,
-                 CODEC_OGG_FLAC, CODEC_OGG_OPUS};
     enum : int { FORMAT_NONE = 0, FORMAT_M3U = 1, FORMAT_PLS = 2, FORMAT_ASX = 3, FORMAT_M3U8 = 4};
     enum : int { AUDIO_NONE, AUDIO_HEADER, AUDIO_DATA,
                  AUDIO_PLAYLISTINIT, AUDIO_PLAYLISTHEADER,  AUDIO_PLAYLISTDATA};