Followup to #7750, #7826

Also reformat and document

From @ejtagle, originally #7459

[2.0.x] Fix broken M600 resume_print

[2.0.x] Option to disallow motion before homing

Derived from #7811 and #7779

Cleanup 2.0.x compiler warnings

gitignorefix

Fix G10/G11 with synchronize

Marlin 2.0.x - fix LPC1768 stepper hang and limit maximum stepper ISR spacing

[2.0.x] Fix Servo class compile errors

[2.0.x] Fix LPC1768 USB interrupt priority

2.0.x Re-ARM compile issues - work around

Marlin 2.0.x - M355 fixes & LCD improvements

fix Travis error

[2.0.x] Show leveling status on character LCD

[bugfix-2.0.x] Fix compiler error (issue #7730)

[2.0.x] HAL for STM32F1

[2.0.x] User menu return-to-status option

Adding files for STM32F1 HAL based on libmaple/stm32duino core.
Current persistent_store uses cardreader changes to be sent in separate
commit, but could be changed to use i2c eeprom.

Some HAL formatting cleanup

Fixes for GT2560, ANET A8

Fixes for 2 "... not declared in this scope" compiler errors.

For PR #7738

[2.0.x] Fix G3D_PANEL encoder steps, babystep label #7762

Comes from #7760

Comes from #7760