Update the set_position() method to convert from millimeters to
absolute step position.
Also, update PrinterStepper.get_homed_offset() and
mcu_stepper.get_commanded_position() to return millimeters.
Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
Rename step_sqrt/step_factor to step_accel/step_const and have them
directly take the velocity and acceleration in millimeters and
seconds. This simplifies the kinematic classes.
Signed-off-by: Kevin O'Connor <kevin@koconnor.net>