Major fix!

Fixes

• New calibration method, for the previous one was always locking the code in an infinite loop.

Diffs

• Remove calibration for the accelerometer.

Improvements

• Add suggestion on #6 (comment) ;
• Remove dependency on String objects (consequence of changing calibration method), as suggested by jremington at https://forum.arduino.cc/index.php?topic=633172.0 .

Future

• Change calibration method (again) in order to assure better accuracy.