The old P112 plugin was 4 years out of date and did no longer compile.

It also did not include recent improvements of the P003 Counter plugin
on which it was originally based.
This is a fresh copy of the P003 plugin with the P112 changes added.
Furthermore, a few bugs were squashed.
A better debounce algorithm has been added.
Outputs of power and energy are now both in W and Wh units.
They are correctly scale based on the pulses/kWh setting.