实现音频文件播放，暂停，前进，后退，播放列表，添加单个文件，及文件夹到播放列表，删除播放列表，播放时间显示，滑块控制等。-Achieve the audio file play, pause, forward, backward, play list, add a single file, and folder to the playlist, delete playlist, play time display, slider con