Detail for my Mk2_RFdatalog_1.ino sketch

This is an upgraded version of the original Mk2 sketch for use with my
PCB-based hardware.  It supports two current sensors, CT1 and CT2.  
CT1 is for monitoring the flow of energy at the supply point; CT2 is 
available for monitoring the flow of current to the primary dump-load.  

With this version, datalog messages are routinely transmitted by the
on-board RF facility.  By using the pin-saving hardware option, the 
4-digit display is still available for use.

The payload of the transmitted data has three integer fields:
- the message number, which increases by one every time;
- the power at the supply point in Joules (import is -ve, export is +ve)
- the diverted energy total for today, in kWh