This update adds a `dt` attribute to `AsyncRateLimiter`, matching its API better with that of the other `RateLimiter`.
Added
- AsyncRateLimiter: `dt` property
Changed
- AsyncRateLimiter: `measured_period` is now a property
- AsyncRateLimiter: `next_tick` is now a property
- AsyncRateLimiter: `period` is now a property
- AsyncRateLimiter: `slack` is now a property