* Fixed macOS conditional check.
Turns out TARGET_OS_MAC is 1 for macOS and iOS, we should be using
TARGET_OS_OSX instead.
Tweet with some history: https://twitter.com/gparker/status/836341915037515778
* Update README.
* Add GULUserDefaults to GoogleUtilities.
This is a workaround for NSUserDefaults crashing when setting values
in the background in some situations on iOS 11. This uses the C API
in order to avoid an NSNotification firing (which a class eventually
tries to update the UI from the thread that set the value).
* Add missing copyright information.
* Resolve macOS issues, address feedback.
* Removed unnecessary enum value.
Paul Beusterien