Flickr-photos-api

* Flatten the definition of `MachineTags`, to simplify queries for a namespace/predicate pair.

* Export the new `MachineTags` type as a top-level type.
It can be imported as `from flickr_photos_api import MachineTags`.

* Add support for machine tags

Machine tags will now be parsed in the list of tags, and presented as a structured object in the `machine_tags` field.
This does not change the existing `tags` field, just provide a convenient way to query machine tags.

* Fix a bug in the new `post_comment()` method.

If you try to post a comment on a photo that doesn't exist, you now get a `ResourceNotFound` exception rather than an `UnrecognisedFlickrApiException`.

* The constructor on `FlickrApi` has changed.

Previously:


from flickr_photos_api import FlickrApi

FlickrApi(api_key: str, user_agent: str)


Now:


from flickr_photos_api import FlickrApi

FlickrApi(client: httpx.Client)
FlickrApi.with_api_key(api_key: str, user_agent: str)


This is to make the underlying HTTP client a bit more flexible.

* There's a new method on `FlickrApi`: `post_comment(photo_id: str, comment_text: str)`.

This allows you to post comments on Flickr photos, if you pass an HTTPX client that has OAuth 1.0a set up with Flickr.
See the tests for an example of how this works.

* Retry every error that returns a 5xx status code, not just 500.

For example, a `502 Bad Gateway` error will now be retried where previously it would fail immediately.