add decoder for NonEmptyString

[srghma]

can add after 0.14, because cannot run tests now

instance decodeJsonCodePoint :: DecodeJson NonEmptyString where
  decodeJson = decodeNonEmptyString

decodeNonEmptyString :: Json -> Either JsonDecodeError NonEmptyString
decodeNonEmptyString json =
  note (Named "NonEmptyString" $ UnexpectedValue json)
    =<< map (NonEmptyString.fromString) (decodeString json)

[srghma]

we could also add

decodeNonempty :: Json -> Either JsonDecodeError String
decodeNonempty = map NonEmptyString.toString <<< decodeNonEmptyString

like haskell lib envparse does

they have str :: String and nonempty :: String

[thomashoneyman]

I think this is sensible to add, and I'd accept a PR for it. If you don't want to build using a 0.14 release candidate you could always check out the last commit before the 0.14 changes, make your update, and then rebase onto master (I think, at least).