The image_url method makes a request to `https://seiga.nicovideo.jp/images/source/:image_id`
to see where this URL redirects to. Before we did a GET request, which caused it to download
the full image. This could fail with a timeout error if the download took too long. We also
cached the request, which caused the full image to be cached, even though we only need the
headers. Change it to a HEAD request so we don't have to download the entire image just to
check the URL.
Replace http.rb's builtin redirect following option with our own
redirect follower. This fixes an issue with http.rb losing cookies after
following a redirect.
3cdf67920 changed it so that Danbooru::Http follows redirects by
default. This broke some things in the Nico Seiga strategy, so disable
following redirects in the Nico Seiga API client for now.
Also change it so that Danbooru::Http follows redirects after a POST
request (by setting `strict: false`). Nico Seiga needs this because it
sends a redirect after we POST the login form.
* Get rid of mechanize, fully switch to Danbooru::Http
* Switch to mobile api, improving speed
* Merge main and manga clients
* Add full support for manga pages
* Add support for anonymous and r-15 images
* Don't fail when attempting to upload oekaki direct links
* Various misc fixes
* `summary` is the wrong field. It's the list of comments left by users,
not the artist's commentary.
* For some reason `doc.response.image.description` returns nil even
though the description element exists. Switch to `Hash.from_xml` to
avoid this.
