stringprep?

I'm wondering if you would accept a patch to add stringprep? I know RFC3920 is a bit dated, but it is still what most of the world is using. Cons: it would be a breaking change to the API. Pros: you would not have to break the API again when you got to RFC7622.

Anyway, if you're willing to accept stringprep, I'll get started on it.

Thanks!