Add more Fold1 instances

[Topsii]

I omitted Costrong and ArrowLoop instances for Fold1. Fold already has a Costrong instance, but similar to the Monad instances mentioned in #214 (comment) I wonder whether it is safer to omit them to ensure Fold1s are streaming constant memory.

instance Costrong Fold1 where
    unfirst p = fmap f nonEmpty
      where
        f as = b
          where
            (b, d) = Control.Foldl.NonEmpty.fold1 p $ do
              a <- as
              pure (a, d)

instance ArrowLoop Fold1 where
    loop = unfirst

I also added nest for Fold1 and distinguished between both and both1 in the doctests.