ex. 5.13 - map via unfold - directly matching on stream instead of headOption
ex. 5.13 - map via unfold - directly matching on stream instead of headOption -> pattern match replaced by anonymous pattern matching => solution given
ex. 5.13 - take via unfold
ex. 5.13 - take via unfold implemented
ex. 5.13 - takeWhile via unfold implemented
ex. 5.13 - zipWith tests
ex. 5.13 - zipWith