change sign of z adjustment based on observation
refactored accleration in zprobe to avoid race conditions where other speeds are set by mistake
added some comments and minor refactor of steppermotor - re 32bit fixed point vs 64bit fixed point
tweak probe speeds
add docs
add ability to save the bed plane with M500 and config setting to enable that
M503 will inform user if bed plane will be saved
Merge pull request #471 from wolfmanjm/feature/three-point-bed-levelling-strategy

Feature/three point bed levelling strategy
Merge commit 'd0364eb3396c313ef0e51f4387f276b701bd1e64' into Egde