0.0.1

• Receiving FCM messages while the application runs, on a tap from the
  background and on a launch from a notification.
• A local copy of a message that arrives while the application runs, in an
  Android channel given by the application.
• Taps as a stream and the launch notification as a single value.
• The FCM token and a stream of its changes.
• Requesting the notification permission and reading its current state.
• Showing a local notification from the application.
• Web support: foreground messages, local copies, taps and the token for a
  vapidKey.