first main sketch check-in

basically the Bridge sketch!
major change implement heating code!

Thermo readout now works
Basic heating loop now works.
Heats with relay until cutoff, then uses theristor to get the rest of
the way.
Absolute safety temperature cutoff is also implemented and lightly
tested.
Some Serial.print code was introduced, remove this at a later date
(maybe with #DEBUGs?)