Bump to version 7.2.1

Release 7.2 (pusher#347)

* Add php 8.1 to CI

* Bump to version 7.2.0

* Update readme

Co-authored-by: Pusher CI <pusher-ci@pusher.com>

Prepare for release of 7.1.0-beta (pusher#333)

* Prepare for release of 7.1.0-beta

* Update CHANGELOG.md

Prepare for release of 7.1.0-beta (pusher#333)

* Prepare for release of 7.1.0-beta

* Update CHANGELOG.md

Merge pull request pusher#317 from pusher/develop

Develop

Merge pull request pusher#307 from pusher/develop

Develop

Merge pull request pusher#305 from pusher/develop

Add type signatures, refactor

Merge pull request pusher#298 from pusher/async

Async

Merge pull request pusher#297 from pusher/fix_interface

Use type hints, document Guzzle Exception

Merge pull request pusher#289 from pusher/guzzle

Switch to Guzzle for HTTP calls