Enable all old_z_*_endstop vars for Z_DUAL_ENDSTOPS

- Potentially addressing #1911

Rename servos[] array in Marlin to servo[]

Fix type of code_has_value

Naming and code comments

Fix Syntax Error Filament Runout Statement

Several fixups

- Change some `previous_` time vars to `next_` so an add only happens
at intervals
- Fix `HEATER_0_USES_MAX6675` polling too frequently, or not at all

Conflicts:
	Marlin/ultralcd.cpp

Manual bed leveling menu fixes.

Homing fixes

lcdDrawUpdate = 2 helped a lot!

- 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)

Fix doubled lcd_quick_feedback

- MENU_ITEM causes lcd_quick_feedback to be called, so only those calls
to `lcd_goto_menu` outside of the `MENU_ITEM` macro need to set the
`feedback` flag when calling `lcd_goto_menu`.

machine name for hephestos too

Apply CUSTOM_MACHINE_NAME to configs

- Replace “Mendel” with “RepRap”

Latest upstream commits

Break out prevent_dangerous_extrude feature

- In GCodes.md

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

Fix moves for DELTA for MANUAL_BED_LEVELING

Latest upstream commits

- Use `line_to_current` in place of `plan_buffer_line`