Gather some statistics (like unix `time`) during running and output when process stops

[jrudolph]

Potential fields when process is started:

• Start time
• PID

Potential fields when process is running (for showing with reStatus):

• Start time, run time
• CPU usage
• Mem usage

Potential fields when process is stopped:

• Start time, end time, (wall-clock) run time
• CPU usage
• Max mem usage

The difficulty might be getting the PID but if we have that we can probably go to proc for the other things.