Option to use an ESP8266 instead of a Wiznet W5100

[T-vK]

It would be nice to have the option to use a different network interface. For instance an ESP8266 based module instead of a Wiznet W5100 based Ethernet Shield. It would be even better if this project would work when flashed to something like an ESP-12 directly. Most Arduino libraries are already compatible anyway, so this should be straight forward. This way we wouldn't have to wait until someone starts working on wot-esp8266.