initial ch08 commit
ex 8.3
ex 8.4, 8.5
Merge branch 'master' into ch08
ex 8.6
ex 8.7, 8.8
ex 8.8
ex 8.9
ex 8.9 tag enhanced for '||' combinator
ex 8.10
ex 8.12
ex 8.12
ex 8.14
ex 8.14 book solution fixed
typos
check added.
Playing with Par combinators
ex 8.16, 8.17
ex 8.17