* Add Auth interoperability library.
This allows other SDKs to retrieve the user ID and fetch a new
Auth token in a type-safe way through the Core container.
* Remove unnecessary import.
* Add missing copyright.
* Resolve comments.
- Remove unnecessary umbrella header.
- Move to version 1.0.
- Add tvOS support for app lifecycle changes.
* Move public interop headers to private.
* Add public_header_files too.
* Moved headers back into public.
* Shorten Interoperability and Interoperable to Interop.
* Add AuthInterop to travis linting.
* Fixed tag format in AuthInterop.podspec.
* Add AuthInterop path to Firestore Podfile.
Paul Beusterien