adds operator-> to accumulate
adds operator-> to accumulate

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