initial ch10 commit
ex 10.1, 10.2, 10.3
ex 10.4
ex 10.5, 10.6, 10.7
ex 10.8
ex 10.9
ex 10.10, 10.11
ex 10.12
ex 10.13, 10.14
ex 10.13, 10.14, 10.15
Merge branch 'ch10' of https://github.com/zaphod66/myfpinscala into ch10
playing with Foldable
ex 10.16, 10.17
ex 10.18
played with MonoidWS