Adds = default for copy ctor
Adds = default for copy ctor

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