Moves range step check to range function
Moves range step check to range function

Also compresses separate Range constructors into one

tempbottle/cppitertools,ryanhaining/cppitertools,jkhoogland/cppitertools,tempbottle/cppitertools,jkhoogland/cppitertools,jkhoogland/cppitertools,ryanhaining/cppitertools,tempbottle/cppitertools,ryanhaining/cppitertools