Clarify which PID values to enter

Update menu plan

Fixed typo.

Various typo fixes #3 - only in comments, no code changes.

Updated gen3+ board pins names to current convention

Users can be confused as to which values to enter after a PID tune. Updating the message to help clarity it.
New message: "PID Autotune finished! Put the last Kp, Ki and Kd constants from above into Configuration.h"

Old message: "PID Autotune finished! Put the Kp, Ki and Kd constants into Configuration.h"

Auto bed leveling at arbitrary points

Fixed compiler errors on Ubuntu using arduino-core

Use constants instead of numeric literals

Prevent G29 without first homing in X and Y

If position is unknown, then G29 can be dangerous.

Added dutch to language.h

This reverts commit 51ae4881.

Fwretract fixes, cleanup

Fix compile error

Add whitespace to M114 output

Various typo fixes - only in comments, no code changes.

Various typo fixes #2 - only in comments, no code changes.

Marlin v1

Makefile fixes