Request hardware info on initialisation

This sends the HW_REQ_INFO request to the device immediately after opening the serial port. A short period is waited for a response to the message. The hardware info is populated in a new hwinfo property of APTDevice and so should be available to every subclass.

The intention is that the device information is available to query immediately upon initialisation, allowing the serial number to be checked in order to differentiate between multiple identical devices in cases (e.g. Windows) where the serial_number property of the serial device is not implemented by pyserial and/or the operating system. Note however that the first device I tested on (a MFF02) reported 0 as its serial number. I will test on some other devices to see if that's just an anomaly.