add API to easily create a new Structure from iterator

I'd like to copy a structure while filtering some of its fields. Ideally I'd like to do something like:

let s2: Structure = s.iter().filter(|(name, _value)| *name == "badger").collect();

I tried implementing FromIterator on Iter but that's not working as Iter yield (&'static str, &glib::SendValue) and so we lose the structure name along the way.

@slomo : what would be the proper way to do that?