How should group_imports handle visibility?

[camsteffen]

1. What should be the default behavior with how imports are grouped by visibility?
   1. Should pub items be sorted differently at all?
   2. Should pub(<visibility>) be sorted differently than pub?
   3. Sort by visibility then by name or just by name? What about pub(in a::b)?
   4. Should pub(<visibility>) cause more blank-line-separated groups? (e.g. a pub group and a pub(crate) group, etc.) or just one group for all pub items?
2. What config options should be available?

[camsteffen]

IMO sorting pub items separately should be on by default with group_imports. I think having pub items first is much more desirable than mixing them together with non-pub items.

• Put all pub items (visible to other crates) in one group
• Put all pub(..) items (visible to somewhere within the crate) in another group.
  • Within the pub(..) group, sort by visibility (most visible first), then by import name.
  • Sort pub(in <mod>) last within the pub group, and sort those by the visibility mod, then by import name.
  • Sort visibility mod with pub(in {crate,super,self}::<mod>) before those without a keyword prefix.