Added EmonTH sketch with automatic onewire bus scanning up to 60 sensors

Added EmonTH sketch with automatic onewire bus scanning up to 60 sensors. Also updated the readme accordingly. This code has been running for a few days with no problems and I believe it to be stable.

Also changes update interval timing from minutes to seconds as you will probably want to transmit every 15 secs to 10 min on the multiple onewire sensor sketches.