Attempt to fix battery drain issue affecting some emonTH2 units by switching to use of minimal RFM69_LPL library which has more timeout checks on while loops alongside an option to not wait for channel clear before sending data.
Current consumption measured to be 4% lower so far on this version due to other timing optimisation but this is not related to the battery drain issue.
Pulse counting and external temperature sensing disabled by default. Enable via serial configuration.