Add firmata ethernet adaptor.

Firmata Ethernet Adaptor could be created as the usual one, but with
socket address instead of port.

Usage:
firmataAdaptor := firmata.NewFirmataEthernetAdaptor("arduino",
"192.168.0.13:5000")
Merge pull request #1 from Yanzay/firmata-ethernet

Add firmata ethernet adaptor.