/// <summary>
 /// Error handler function
 /// </summary>
 /// <param name="e">The exception</param>
 private void Error(GenericEventArgs <Exception> e)
 {
     this.OnError?.Invoke(this, e);
 }
 /// <summary>
 /// Called when a TTS requst has been successfully completed and audio is available.
 /// </summary>
 private void AudioAvailable(GenericEventArgs <Stream> e)
 {
     this.OnAudioAvailable?.Invoke(this, e);
 }