Bump to 1.6.0 (TakeScoop#186)

Xcode 10 / Swift 4.2 support

Key generation support + Swift 4.1 & Xcode 9.3

Fix Xcode 9.1/9.2 warnings

Swift 3.2/4.0 support, errors as enum

Private key header stripping + ObjC layer

Fix Carthage integration

Added Key.reference, Key.originalData, Key.data(), Key.pemString(), K…

…ey.base64String(), Key(reference:)

SwiftyRSA grand refactoring. See CHANGELOG.md for more information

Swift 3.0 + None padding fixes