- Address issue raised in #1961

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.

- 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`

- Document `manage_inactivity` function
- Allow `EXTRUDER_RUNOUT_PREVENT` to work with all extruders
- Use faster `memcpy` for copying coordinates