API for CPU time / memory usage

[Mathnerd314]

It would be like waitForProcess, except returning a statistics list.

On Linux/BSD, this is the wait4 system call. On Windows, these can be extracted with GetProcessMemoryInfo/GetProcessTimes similarly to the exit code. On Mac, wait4 returns the times, but getting memory statistics requires a tricky Mach task info call which probably doesn't work on dead child processes (and I have no easy way of testing it).