v3.3.0: Swift 3 and stability

This release fixes an issue where the apiKey property has an ambiguous translation into Swift 3. A number of methods and properties have been updated to follow the Swift 3 API Design Guidelines. Swift 2.x project should be able to continue to use the existing method and property names.

Xcode 8 is required to build projects using this release, and iOS 7 devices are no longer supported. Several deprecation warnings have been fixed for projects targeting iOS 8 and later.