Cleanup Warnings

No logic changes. Cleans up some retain warnings w/ explicit self.

Xcode 9 support

A minor release to take care of Xcode 9 and a couple of other small build fixes.

• Remove non-modular header from framework header #11
• Add watchOS and tvOS support. #8
• Upgrade to build on Xcode 9b1

v3.0.2: New repository

Extracted from Swift repository.

Applied a minor security fix to check HMAC prior to final decryption rather than after. There is no known vulnerability that this addresses, but it is slightly better hygiene. Thanks to @doRadiology.

Updated Xcode project to better handle Xcode 8.