下载语音接口：
//下载语音

    function down_voice(voice){
        if (voice.media_id == '') {
            wwToast("{:L('send_voice_upload_voice_null')}");
            return;
        }
        wx.downloadVoice({
            serverId: voice.media_id,
            success: function (res) {
                voice.localId = res.localId;
            }
        });
    };
    
    顺便分享一个微信接口的网址：http://www.cnblogs.com/txw1958/p/weixin-js-sdk-demo.html
    
    如果下载语音不行，可以保存永久素材吗？求详解