Light messaging using serial.

Open port, set up handler for received data, send stuff. This PowerShell script \Test-SerialPort.ps1 is used for testing

convert to library for use by other programs. But needs to be small, quick, efficient.

• Turn into a proper class
• lockimg

Include new fields, all 1 byte to save space

• error checking - in progress
• length field?
• source, destination fields (for Easy Radio http://www.lprs.co.uk/easy-radio/what-is-it-and-why-use-it.html)