Detail for my Mk2_withRemoteLoad_2.ino sketch

This is an upgraded version of the original Mk2 sketch for use with my
PCB-based hardware.  It still 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, a secondary dump-load is supported, it being controlled 
by the on-board RF facility.  By using the pin-saving hardware option, 
the 4-digit display is still available for use.

The primary (wired) load is still controlled from the "trigger" port.  In 
this sketch, the "mode" port is now used for priority selection.  If the 
associated switch is open, the local (wired) load has priority.  If the
switch is closed, thereby shorting these pins together, the secondary 
(RF-controlled)load has priority.

The _2 release includes various changes since the _1 version:

- a REQUIRED_EXPORT_IN_WATTS facility has been added.  This acts like a 
  leak in the energy bucket, therefore reducing the amount of surplus power 
  that can be diverted.  When a negative value is entered, this facility
  acts like a PV Simulator, which can be very helful for test purposes.

- The state of the energy bucket is displayed at the Serial Monitor every 
  second in Joules.

- The RFM12B is no longer sent to sleep between RF trnsmissions, it remains
  awake throughout.  The library call rf12_sendStart() has been replaced by
  rf12_sendNow().  These changes are intended to minimise any disruption
  to the continuous sampling process when RF transmissions are sent.