toString

util.ms2str();
util.ms2str(, '');
 * mode:
 *   0: auto
 *   1: s
 *   2: ms
 *
 * unsigned:
 *   true : No '-' regardless of positive or negative
 *   false: With '-' for negative value
 *
 * zero:
 *   Set true to padding zero
 *
util.ms2time(millis, mode, unsigned, zero)
util.ms2time();
util.ms2time(, );
util.ms2time(, , );
util.ms2time(, , , );