Add option to scan attached probes

[cr1901]

Context

There should be an option to scan probes, just like there's an option to scan attached devices. At minimum, for FTDI devices, I think this should return the serial number so that

Furthermore, libftdi failing to open a device on Windows does not indicate a fatal error. There are multiple types of device drivers for FTDI devices on Windows, and a failure to open may indicate that a probe is using a driver that libftdi doesn't understand. Therefore, I believe scanning probes should have an option to keep going on error.

[trabucayre]

I have pushed a first draft. Only tested with FTDI (and clone) devices.
Theoritically all devices with VID/PID listed in cable_list may be discovered but I have to add a search in board_list for DFU devices.
And since cable description is limited to vid/pid is not possible to be more precise for FTDI device (ie digilent_hs2 vs bus_blaster vs tigard vs ...).

[trabucayre]

Is it good to you? Can I close this issue?
Thanks

[cr1901]

Yes, it's safe to close this issue, the new functionality does what I want :).

[trabucayre]

Thanks!