[Firmware] clarified meaning of Hall and encoder

-hall_Get(): renamed to hall_GetVoltage() and changed the documentation to
make it more clear. The voltage returned now corresponds to the Hall output
pin, not the ADC pin, which was not meaningful.
-Renamed hapt_motorPosCod to hapt_encoderPaddleAngle, in order to avoid a
confusion between motor shaft angle and paddle angle.
-enc_GetPosition() now returns the motor shaft angle, instead of the
paddle angle. The conversion to paddle angle is performed in
haptic_controller.