v2.1

• Ensure backdrop is always initialized during startup (#90).
• Don't attempt to use window persistence in un-packaged applications.
• WebAuthenticator: now supports cancellation tokens.
• WebAuthenticator: Avoids an issue where state parameters are not always correctly handled/preserved correctly by OAuth services (#92).
• Persistence: Add support for custom Window state persistence storage, for use by unpackaged applications (#61).