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- Rates are now counted in fixed—instead of sliding—windows, except for
per-second limits. See the Upgrade Notes.
- Mixin renamed to `RatelimitMixin` (lowercase `l`) for consistency.
- Dramatic rewrite.
- `ip`, `field`, and `keys` arguments replaced with `key`.
- well-known "key" values support.
- Custom callable rate functions.
- Support for "not limited" rate.
- Replaces ``skip_if`` argument.