Add more serial:// options

[wybiral]

~The serial package being used supports multiple options beyond the baud rate which might be useful to expose as optional arguments.~

We should add more options to the serial protocol. See comment below.

[wybiral]

That serial package is no longer being used in v2 because of #27

The one currently being used is this package.

Good options to provide would probably be:

• Data bits (maps to serial.Config.Size)
• Parity (maps to serial.Config.Parity)
• Stop bits (maps to serial.Config.StopBits)

The current defaults are for 8-N-1. It's probably a good idea to look at other tools that take in these options and see if there's an implied standard for supplying these.