Enabled gcc compiler warnings. Fixed over 100 warnings including at
least one actual and several potential bugs.
Simplified delta calibration code and added X and Y parameters to M665
command
Implemented chamber temperature commands (thanks chrishamm)
Tidied up delta auto-calibration code. We now use least squares for 3,
4, 6 or 7-factor calibration.
When doing delta calibration, if a probe offset was used to adjust the
head position when probing, use the actual head coordinates instead the
probed coordinates.
Bug fix: newline was missing at end of SD card file list sent to USB
when in Marlin emulation mode.
Bug fix: Heater average PWM report (M573) sometimes gave inaccurate
values when the S parameter was used.
