Single twisted-pair full-duplex support

[renne]

Smarthome setups suffer from a lot of wires to install. Using single-pair full-duplex ethernet would allow easy installation with high data rates and MQTT protocol (TCP/IP).

Transmitting Full-Duplex Data over a Single Twisted Pair Cable shows how to use an ISL 32705 RS485 transceiver for full-duplex on a single CAT.5 twisted pair.

Please adjust your circuit to support full-duplex ethernet on a single CAT.5 twisted pair.

[cnlohr]

For my purposes, half-duplex was more than sufficient, and allowed consistent two-way communication, but using a proper line driver would be a huge benefit.

Please test the implementation against espthernet, make modifications to the Readme to include the changes and do a pull request.