let hcat, hsep and vcat work with Foldables

[KommuSoft]

[phadej]

This is technically a breaking change (e.g. vsep [docA, docB] with OverloadedLists enabled), so I don't think this change pulls it weight, there are barely any reasons to make major version of pretty.

When there are some other reasons for major version bump, sure.

[KommuSoft]

I see, would it be an option to create a vsep' etc. that works with Foldables. When I used this in code, I had to convert an item to a list first, which is of course not problematic, but is not really necessary.