Version 0.3.0

Release 0.3.0

• Addition: A very basic Flask app that can be used to validate
  happy flows for registration and verification/signing.
• API Change: fido_u2f.device.DeviceRegistration is no longer
  required to be subclassed for a device to be valid. It's
  still recommended to subclass it however as it adds nicer error
  messages if the implementation is missing required properties
• Fixes typing problems during signing/verification.