Add `sync_plan_position()` after `axis_is_at_home(axis)` to keep the
planner position in sync when homing.

This makes `M421` more amenable for irregular matrices

Corrected "servo.h" to "Servo.h" because of the updated filename.

This addresses comments in #1956 and #1079. In particular, this is useful
when both endstops are stationary on a CoreXY system, and the Y axis needs
to be homed before the X so the flags are aligned.

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

- Address issue raised in #1961

Else will throw error:
@:0 B@:0
Error:No thermistors - no temperature
[ERROR] Error:No thermistors - no temperature

when no bed is defined

Ensure the probe offset will always be included when homing Z.

c'n'p ftw :/

no user will home to 0 with a max endstopp

Centralised beep code to lcd_buzz().
From gcode_M300() and lcd_quick_feedback().

Enforced max. duration for M300 to 5 seconds.

Corrected description in 'Configuration.h'

LCD_FEEDBACK_FREQUENCY_HZ 0 gives now a silent delay of
LCD_FEEDBACK_FREQUENCY_DURATION_MS.

Corrected wrong order of parameters.

Ensure the probe offset will always be included when homing Z.

- Prevent `Z_SAFE_HOMING` from homing Z twice in some cases
- Allow `G28` with XYZ values of 0 to explicitly set the position
- Don’t add `home_offset` when setting XYZ explicitly in `G28`
- Add `code_has_value` function to check for the presence of a numeric
value (could just test for space or nul to allow other types of values)

- It’s inline here, but could be a macro and duplicated for
`planner.cpp`

- Use `line_to_current` in place of `plan_buffer_line`

Resolved some warnings in Marlin_main.cpp regarding compares of signed and unsigned integers by replacing 'int' or 'uint16_t' with 'uint8_t'.

and cleaned typo.

- Address Issue #1682 at hash #issuecomment-89756858

Should be `retracting` and not `retract`