constraint of temps to INT_MIN/INT_MAX made as a dedicated function.
My previous optimization convertAndConstrain returned 32-bit rather than 16-bit quantity. Fixed this. Saves about 50 bytes.
OneWireTempSensor.cpp destructor non inline.
reworked default and user configuration.

To make this work, add
"./fallback"

to the include paths in the avr project. (I've not checked in the project since mine is set up for Uno)