EitherErr Applicative for Functor-Applicative-Monad_Proposal
fix compatibility with optparse-applciative 0.10
  - the `option` API is changed
  - `execParserMaybe` is deprecated
Remove unnecessary import
Merge branch 'suhorng-master'
Merge pull request #1504 from Heather/eithererr

EitherErr Applicative for Functor-Applicative-Monad_Proposal
sharingan