function str2ab(s) {
        var s_utf8 = unescape(encodeURIComponent(s));
        var buf = new ArrayBuffer(s_utf8.length);
        var bufView = new Uint8Array(buf);
        for (var i = 0; i < s_utf8.length; i++) {
            bufView[i] = s_utf8.charCodeAt(i);
        }
        return buf;
    }
Convert a string to array buffer in UTF8
@function str2ab
@memberof Quiet
@param {string} s - string to be converted
@returns {ArrayBuffer} buf - converted arraybuffer