Add gpibscan utility

The gpibscan utility scans all possible GPIB addresses on a serial device with the *IDN? command and returns the response. It is useful for determining what address is set for different devices without physical access to them.

The usage of the tool:

Usage: ./bin/gpibscan [options] usbport

List of options:
 -d, --debug       Enable more verbose printout

Example output:

[kkrizka@triplerock build]$ ./bin/gpibscan /dev/ttyUSB0
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 5: KEITHLEY INSTRUMENTS INC.,MODEL 2410,0883484,C22   May 21 2001 08:33:10/A02  /F/H
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