Various changes

1. Fixed bug introduced at version 57r whereby axis travel limits were
not applied properly.
2. Increased maximum travel on 2nd phase of Z-probing from 1mm to 10mm
3. Added parameters R (thermistor 25C resistance) and B (thermistor
beta) to M301 command
4. Added support for M304 command with same parameters as M301 command
5. PID and thermistor parameters are now saved to flash memory