Auth: request a token without an API key, authCallback or authUrl

[ricardopereira]

Authentication (RSC14c) When a token or tokenDetails is used to instance the library, and no means to renew the token is provided (either an API key, authCallback or authUrl), if the server responds with 40140 (token expired) to a request, the client library should indicate an error and not retry the request.

The spec is not implemented yet.
IMO the error should be different:

Error Domain=io.ably.cocoa Code=40400 "" UserInfo={NSLocalizedFailureReason=Could not find path: /keys/(null)/requestToken, ARTErrorStatusCode=404, NSLocalizedDescription=}

It is not obvious that the client was initialised with a token/tokenDetails and that is why a new token was not retrieved.