Make `basic::GetIterator` public

[ihrwein]

First of all, thanks for working on this library!

I'd like to store a basic::GetIterator value in my struct, but cannot do it since it's private. Can we make that type public? If yes, I'm more than happy to send a PR.

Thanks!

Update: actually the type is public, but its module is private. Reexporting it from basic would be equally good for me.