This addes the command serial_passthru which will pass data from one
device to another. This can be used to use u-center connected to USB
with a GPS on a serial port.
Usage: serial_passthru [arguments...]
-e <val> External device path
values: <file:dev>
-d <val> Internal device path
values: <file:dev>
[-b <val>] Baudrate
default: 115200
[-t] Track the External devices baudrate on internal device
With the -t option baudrate changes made on the PC connected to the USB
will be set to the intrenal device.