Alternative sample reflow oven code

Peter, here is the source code I ended up with. Rather than ask to replace your oven code, it seems to make more sense to contribute it back as an alternative sample. It has some nice features that I find useful (especially the serial port output that reports reflow phase data for tuning the heater patterns).

The lead-free profile is based on what you had in your original code (though I haven't tested it with this code). The lead-bearing profile is based on the Kester "typical" curve, with generally accepted limits for ramp-up/ramp-down times. And of course the lead-bearing profile's heater patterns are tuned for my own oven.