ENH: make commands lower case by default

Source/cmAddCustomCommandCommand.h

Source/cmAddCustomTargetCommand.h

Source/cmAddDefinitionsCommand.h

Source/cmAddDependenciesCommand.h

Source/cmAddExecutableCommand.h

Source/cmAddLibraryCommand.h

Source/cmAddSubDirectoryCommand.h

Source/cmAddTestCommand.h

Source/cmAuxSourceDirectoryCommand.h

Source/cmBuildCommand.h

Source/cmBuildNameCommand.h

Source/cmCMakeMinimumRequired.h

Source/cmConfigureFileCommand.h

Source/cmCreateTestSourceList.h

Source/cmDefinePropertyCommand.h

Source/cmDocumentation.cxx

Source/cmElseCommand.h

Source/cmElseIfCommand.h

Source/cmEnableLanguageCommand.h

Source/cmEnableTestingCommand.h