Add Serial class to Lua API

[cesarvandevelde]

A class for serial communication should be added to the Lua API. This would be useful for communicating to USB-serial devices such as an Arduino or a USB bluetooth dongle, opening up new avenues for hardware/electronics hacking.

I have already made a preliminary attempt, but this code is completely untested and is consequently commented out. It can be found at the bottom of /apps/luascripting/scripthost.py.