Return an array with current system resource usage statistics,
as returned by the getrusage(2) of Unix.
namely: utime, stime, maxrss, rus.ru_ixrss, rus.ru_idrss,
rus.ru_isrss, rus.ru_minflt, rus.ru_majflt, rus.ru_nswap,
rus.ru_inblock, rus.ru_oublock, rus.ru_msgsnd,
rus.ru_msgrcv, rus.ru_nsignals, rus.ru_nvcsw,
rus.ru_nivcsw
This function is optional.