Detail for my demo_bothDisplays.ino sketch

This sketch comprises just the display section of my Mk2 PV Router code.  
Its intended purpose was to provide an easy way of checking the operation 
of the 4-digit display, but the later sketch segCheck_bothDisplays.ino 
is more suitable for this task.  

This original version is mentioned in the Build Guide so can remain here 
for completeness.