Merge pull request #3090 from thinkyhead/rc_spelling

Marlin/Conditionals.h

Marlin/Configuration.h

Marlin/Configuration_adv.h

Marlin/Makefile

Marlin/Marlin.h

Marlin/example_configurations/Felix/Configuration.h

Marlin/example_configurations/Felix/Configuration_DUAL.h

Marlin/example_configurations/Felix/Configuration_adv.h

Marlin/example_configurations/Hephestos/Configuration.h

Marlin/example_configurations/Hephestos/Configuration_adv.h

Marlin/example_configurations/K8200/Configuration.h

Marlin/example_configurations/K8200/Configuration_adv.h

...le_configurations/RepRapWorld/Megatronics/Configuration.h

Marlin/example_configurations/RigidBot/Configuration.h

Marlin/example_configurations/RigidBot/Configuration_adv.h

Marlin/example_configurations/SCARA/Configuration.h

Marlin/example_configurations/SCARA/Configuration_adv.h

Marlin/example_configurations/TAZ4/Configuration.h

Marlin/example_configurations/TAZ4/Configuration_adv.h

Marlin/example_configurations/WITBOX/Configuration.h