+ Added aurweb.auth.AnonymousUser
    * An instance of this model is returned as the request user
      when the request is not authenticated
+ Added aurweb.auth.BasicAuthBackend
+ Add starlette's AuthenticationMiddleware to app middleware,
  which uses our BasicAuthBackend facility
+ Added User.is_authenticated()
+ Added User.authenticate(password)
+ Added User.login(request, password)
+ Added User.logout(request)
+ Added repr(User(...)) representation
+ Added aurweb.auth.auth_required decorator.

This change uses the same AURSID logic in the PHP implementation.

Additionally, introduce a few helpers for authentication,
one of which being `User.update_password(password, rounds = 12)`
where `rounds` is a configurable number of salt rounds.

Signed-off-by: Kevin Morris <kevr@0cost.org>