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

Use language.h for "bed"

This should make it safe to enable FWRETRACT by default, with
autoretract (which should now be fixed) only enabled by M209. FWRETRACT
should probably now default to enabled (to make G10/G11 and M207-209
available, without changing functionality when they are not used), but
I’ll save that for another pull request/discussion.

This takes the (now working) G10/G11 code and moves it to a function,
which is called by G10 and G11, and also called by G1 if autoretract is
enabled and a retract/recover move is detected.

Refactor of z probing for auto bed leveling