Log-rate-limit

Added

- Add methods `trigger()`, `should_trigger()` and `reset_trigger()` that are used to evaluate rate-limiting and trigger logs. These functions can also be used separately from logging for other purposes, e.g. to trigger custom rate-limited events.

Changed

- Expanded usage examples in documentation, as well as other small improvements.
- Slight spacing change to default summary message.

Added

- Allow summary message to contain `stream_id` and `period_sec`.

Fixed

- Set PyPI package description.

Initial release to PyPI.