Documentation + parse_values() takes a file handle

In order to be able to reuse parse_values(), we have
it take a file handle as a second paramater rather than
hard-coding that we write to sys.stdout
More comments / silently quit on KeyboardInterrupt

To mirror the behavior of many Unix utilities, we'll
suppress the stack trace given by a Ctrl+C KeyboardInterrupt,
and just stop writing output and exit.