Opto Servo Probe

My version of probe, some changes. Used 4 magnets 3*1mm instead of spring. Works good.

// PROBE_ACCURACY at X:145.000 Y:100.000 Z:3.000 (samples=10 retract=2.000 speed=5.0 lift_speed=5.0)
// probe at 145.000,100.000 is z=0.992500
// probe at 145.000,100.000 is z=1.000000
// probe at 145.000,100.000 is z=1.000000
// probe at 145.000,100.000 is z=1.000000
// probe at 145.000,100.000 is z=1.000000
// probe at 145.000,100.000 is z=1.000000
// probe at 145.000,100.000 is z=1.000000
// probe at 145.000,100.000 is z=1.000000
// probe at 145.000,100.000 is z=0.995000
// probe at 145.000,100.000 is z=1.000000
// probe accuracy results: maximum 1.000000, minimum 0.992500, range 0.007500, average 0.998750, median 1.000000, standard deviation 0.002562