Handle conditional typeclass implementations

[Avaq]

Some types have type class implementations only when they have specific inner types.

Some examples:

• Maybe a doesn't necessarily have a Setoid implementation, but any Setoid a => Maybe a (for example a Maybe String) does. This is documented here: https://github.com/sanctuary-js/sanctuary-maybe
• ParallelHook a c doesn't necessarily have an Applicative implementation, but ParallelHook (Future a b) c does. This is documented here: https://github.com/fluture-js/fluture-hooks#ParallelHook

[dotnetCarpenter]

My bad for only testing with String and Number, and didn't see a difference.

There are great examples at all of the Sanctuary provided ADT's README.

Pair:

Z[k].test (Pair (Useless) (Useless))
Z[k].test (Pair (['foo']) (['bar']))

https://github.com/sanctuary-js/sanctuary-pair#readme

Maybe:

Z[k].test (Just (Useless))
Z[k].test (Nothing)

https://github.com/sanctuary-js/sanctuary-maybe#readme

Either:

Z[k].test (Right (Useless))
Z[k].test (Right (['foo']))

https://github.com/sanctuary-js/sanctuary-either#readme

Fluture ???
https://github.com/fluture-js/Fluture

@Avaq I'm guessing that since Future only ever holds a function, a Future's Type Class implementations are always the same? Oh, I forgot about ConcurrentFuture, which is not a Monad.