process_times()
Return a three element f64 array containing the cpu time that has been used by the program and the real time that has elapsed since it was started.
The first element of the result corresponds to "user" time in seconds, the second element corresponds to "system" time in seconds and the third element is the elapsed real time in seconds. On operating systems that can't differentiate user and system time, the system time is zero. On operating systems that can't measure cpu time, the user time is equal to the elapsed real time and the system time is zero.