* Allow Member-level users to vote.
* Don't allow Banned or Restricted users to create favorites any more.
Banned and Restricted users aren't allowed to upvote or favorite any
more to prevent sockpuppet accounts from upvoting even after they're
banned.
Make upvotes public the same way favorites are public:
* Rename the "Private favorites" account setting to "Private favorites and upvotes".
* Make upvotes public, unless the user has private upvotes enabled. Note
that private upvotes are still visible to admins. Downvotes are still
hidden to everyone except for admins.
* Make https://danbooru.donmai.us/post_votes visible to all users. This
page shows all public upvotes. Private upvotes and downvotes are only
visible on the page to admins and to the voter themselves.
* Make votes searchable with the `upvote:username` and `downvote:username`
metatags. These already existed before, but they were only usable by
admins and by people searching for their own votes.
Upvotes are public to discourage users from upvoting with multiple
accounts. Upvote abuse is obvious to everyone when upvotes are public.
The other reason is to make upvotes consistent with favorites, which are
already public.
Like 9efb374ae, allow users to toggle between upvoting and downvoting a
post without raising an error or having to manually remove the vote
first. If you upvote a post, then downvote it, the upvote is
automatically removed and replaced by the downvote.
Other changes:
* Tagging a post with `upvote:self` or `downvote:self` is now silently
ignored when the user doesn't have permission to vote, instead of
raising an error.
* Undoing a vote that doesn't exist now does nothing instead of
returning an error. This can happen if you open the same post in two
tabs, undo the vote in tab 1, then try to undo the vote again in tab 2.
Changes to the /post_votes API:
* `POST /post_votes` and `DELETE /post_votes` now return a post vote
instead of a post.
* The `score` param in `POST /post_votes` is now 1 or -1, not `up` or
`down`.
Side effects:
* The data-current-user-is-voter <body> attribute has been removed.
* {{upvote:self}} no longer works. {{upvote:<name>}} should be used instead.
