With these changes the output of `M503 S0` is all you need to restore
the EEPROM. Building on this it is straightforward to save and restore
the EEPROM state using the SD card or external GCode file.

- Added `M145` to set “heatup states” for the LCD menu
- Added `M420` to toggle Mesh Bed Leveling
- Added `M421` to set a single Mesh coordinate
- Extended `Config_PrintSettings` with added M codes
- Cleaned up some comments here and there

- Add `M111` as a standard option to set the debug level
- Implement `DEBUG_ECHO` in `process_commands`
- Other debug levels (e.g., `DEBUG_DRYRUN`) need more work

- Replace “Mendel” with “RepRap”

The automatic versioning system extracts a
build version number from the SCM system

That versioning information is written to the file
_Version.h, a file that is NOT preserved in the SCM.

If such a file will be present,
we include it here to utilize the parameters
that are defined therein.

Catch unlikely but possible error and head crash when using
Z_PROBE_REPEATABILITY_TEST

- Patched up for most included configurations

Z_DUAL_ENDSTOPS is a feature to enable the use of 2 endstops for both Z
steppers - Let's call them Z stepper and Z2 stepper.
That way the machine is capable to align the bed during home, since both
Z steppers are homed.
There is also an implementation of M666 (software endstops adjustment)
to this feature.
After Z homing, this adjustment is applied to just one of the steppers
in order to align the bed.
One just need to home the Z axis and measure the distance difference
between both Z axis and apply the math: Z adjust = Z - Z2.
If the Z stepper axis is closer to the bed, the measure Z > Z2 (yes, it
is.. think about it) and the Z adjust would be positive.
Play a little bit with small adjustments (0.5mm) and check the
behaviour.
The M119 (endstops report) will start reporting the Z2 Endstop as well.

- Add `Conditionals.h` with calculated configuration values
- Add `SanityCheck.h` with checks for configuration errors
- Remove equivalent code from all configurations
- Move error checks from some sources to `SanityCheck.h` also
- Fix initialization of count_direction in stepper.cpp

Automatic selection was to unflexible.

Updated documentation

Updated language files to new logic and documentation.

Updated bdf2u8g.exe

Include of language_en.h now behind national language.

All "#define MSG_STR_*" now surrounded by #ifndef and #endif.

+ May decrease the workload for feature developers. They may omit to
update all the language files but "language_en.h". When loading _en
first, all new features give some display, but the new in English.

- May throw some additional warnings about redefinition during compile.

Select DOGM-displays automaticly.
Give hint where to find charsets.
Add '²' and '³' characters.

This reverts commit 4d5b0e20.

Defined the charsets plus a default.

- Also partial cleanup of Marlin_main.cpp with a smidgen of Doxygen.

- Also adds a language string for the error.
- Also adds SERIAL_EOL as an alias for SERIAL_ECHOLN(“”)