* Add a new method `lookup_user_by_id` for looking up users with their NSID. This allows for slightly faster lookups in cases where you already have the user's NSID, compared to `lookup_user_by_url`.
1.5.7
* Slightly improve the error message you get if you pass an invalid API key.
1.5.6
* Fix another bug in the handling of "date taken" when the value returned by the Flickr API is unusable, e.g. `0000-01-01 00:00:00`.
1.5.5
* Expand the retrying logic, so read timeouts will also be retried up to three times before failing.
1.5.4
* Add some basic retrying logic to the client. If you get a 500 Internal Server Error from the Flickr API, the request will now be retried up to three times before failing.
All other errors will raise immediately.
1.5.3
* Provide a better error when you pass an empty string as a Flickr API key. Now it will fail when you create the client, whereas previously it would fail with an `Invalid API Key` error when you tried to call the Flickr API.