add `foldl1` in foundation's Collection.Collection.Foldable.

[NicolasDP]

It would look like the following:

foldl1' :: Foldable col => (Element col -> Element col -> Element col)
                        -> NonEmpty col
                        -> Element col

Edit: don't implement a the lazy version of this function.

[ndmitchell]

foldl1' is probably a better idea.

[ThreeFx]

Is it wise to force any Foldable to also provide fold1? I am worried that this might prevent some types from having a Foldable instance.