* ItemManager: implement item revisions fetching.
* Fix `UserProfile` member manager and invitation manager.
* Expose `pretty_fingerprint` for pretty fingerprint printing
* Make `deps`/`fetch_options` parameters optional.
* Expose `randombytes` for generating random data
* Expose `API_URL` and add a default parameter to the Client constructor.
* Base64Url: improve the python bindings of this class