Add something like Foldable1 / Traverse1 ?

[aryairani]

These are nice.

[non]

I think instead of Foldable1 we should call it Reducible to parallel the relationship between foldLeft and reduceLeft.

[ceedubs]

I definitely would like to see these type classes.

I do like that Reducible would draw a parallel between foldLeft and reduceLeft. However, in the grand scheme of things, I'm wondering if Foldable1 would be more consistent/clear. Assuming we would have Traverse1/Traverse, the relationship between Foldable1/Foldable might be more clear. We have already chosen to use MonoidK and SemigroupK instead of the scalaz names to express their relationships with Monoid/Semigroup (respectively).

Also people hopefully have a fear of std lib's reduceLeft since it blows up on empty collections ;)

[non]

Fixed in #298.