Windows configurable ReadIntervalTimeout #275

Hi

I would much like some way of configuring win32 ReadIntervalTimeout.

My application uses a fork of serialport-rs:4.2.1 with modified ReadIntervalTimeout to 1 (instead of 0 at that time, which was extrely slow as I recall).

I noticed that you have since changed ReadIntervalTimeout to MAXDWORD, so I retested:

serialport-rs:4.2.1 with modified ReadIntervalTimeout to 1 :
transfer rate 31.5 kbytes/s

serialport-rs:4.7.2
transfer rate 20.5 kbytes/s

(FYI: Both tests run with registry setting "SYSTEM\CurrentControlSet\Enum\FTDIBUS\VID_nnnn+PID_nnnn+nn\0000\Device Parameters" = 1)