Make the MotionPlanner use coordinate rounding

[Wallacoloo]

It's often impossible to locate the printhead at the exact cartesian coordinates requested. When this is the case, the MotionPlanner just moves as close as it can linearly to the destination without passing it. This leads to cases where the printhead is located, say, .5mm before the destination when executing just one more step would put it a mere .1mm overshoot. In my opinion, the latter is more ideal.

So, the MotionPlanner behavior should switch from going "as close to the destination without passing it" to "As close to the destination as possible."