#3631 broke z dual endstops. Solved by @Nocturnal42 in https://github.com/MarlinFirmware/Marlin/issues/5078#issuecomment-256572248

Followup to #5090

・Add header
・Adjust spacing

.) Use already existing inverse_millimeters instead of /
block->millimeters.
.) Prevent overflow during acceleration calculation by checking if float
is necessary. Idea modified from Sailfish.
.) Save two uint32_t or even float multiplications by checking if
step[AXIS] has steps and if max acceleration is lower than accel. If
not, there is no need to check this axis.

MSG_INFO_PRINT_TIME is still being used

As pointed out by #5044

As requested in #5031

We don't want to have retract/prime movements done with LIN_ADVANCE, that's also true with simultaneously executed Z-hops.

With this formula, a start value for K for further fine-calibration can be calculated.

As noted by https://github.com/MarlinFirmware/Marlin/pull/4971#issuecomment-252503295