[swift-evolution] [Proposal] Remove force unwrapping in function signature.

[Ben Rimmington]

Adrian Zubarev wrote:

> Yes please, current Swift 3 Snapshot translated a lot of
> C functions from not optionals to optionals just because
> let and var works correctly on UnsafeMutablePointer’s.

I think this is due to:

* "SE-0055: Making pointer nullability explicit"
  <https://github.com/apple/swift/pull/1878>

* IUOs for code without "nullability annotations"
  <https://developer.apple.com/swift/blog/?id=25>

-- Ben