No need to include timer.h twice
Decouple reflow regulator from UI

Add the simple scheduler, allowing the reflow regulator to run
continuously now (even for standby). (obsoleting timer.[ch])
Verified that the 1-wire thermocouple interface works.
Some UI tweaks (some things temporary missing in bake mode because of
restructuring).
Reflow loop now runs 4 times per second, PID still needs tuning!
Oversampling of internal ADCs.
Timing macros replaced.
Read 1-wire thermocouple cold-junction temperatures.
Added gain and offset adjustments at the top of reflow.c (still
compile-time adjustment).