P2 OAuth2 Versions Save

• Improved error handling
• Make updateFromKeychainItems open

Now uses Swift 4.0 and requires Xcode 9.0, thanks to @paulw11 !

• Implement custom authorization UIs for password grants (thanks @amaurydavid !)
• Allow more UI customization via authConfig.UI and making OAuth2Authorizer friendlier to subclassing
• Optionally allow DataLoader to follow 302 redirects automatically (on same host)
• Fix a bug with data loader not using refresh tokens (#184)

• Move secretInBody and customParameters from authConfig to clientConfig, where they belong
• Allow to override default UTF-8 encoding of the Basic authorization header
• Improvements to embedded authorization
• Remove onAuthorize and onFailure callbacks, which have been deprecated with 3.0 (now handled in the callback to authorize())

• Add Azure flow (thanks @everlof)
• Add keychain_account_* settings (thanks @aidzz)
• Workaround for Safari issue (thanks @everlof)