API

• Add support for phone sign in.
• Remove deprecated create_config function, use
  firebase_config.
• Fix issue with persistence
  #14
• Upgrade firebase.js to modular, tree-shakable version 9 (latest)
• Use packer to bundle with
  webpack for better performances and load time.
• Clean up core class, deprecating several (genuinely) useless
  methods.
• Deprecate useFirebaseUI in favour of firebaseUIContainer.
• In useFirebase deprecate analytics and firestore arguments.
• Breaking FirebaseEmailLink the method called send has been
  renamed to send_email: this method was overwriting an internal
  private method, actually breaking many things.
• Added Storage class to use
  Firebase Storage,
  requires the user to be signed in.
• Added Analytics class to use
  Firebase Analytics
• Add ability to use environment variables instead of the firebase
  config file
  #15
• New documentation site
• FirebaseEmailLink the config method is no longer compulsary;
  redirect URL is dynamically fetched.
• Fix #17
  remove babel breaks polyfill.
• Modular approach implemented: dependencies are rendered
  client-side only where needed.