A major new feature release, see release announcement.

• Feature: Add new Async component to core components.
  (#458 by @clue)

• Feature: Support PHP 8.1 release.
  (#451 by @clue)

• Improve documentation, update HTTP server example for reactphp/http v1.6.0 release.
  (#449 and #459 by @clue and #457 by @nhedger)

• Improve test suite, support PHPUnit 9 and update dependencies to avoid skipping tests.
  (#450 and #454 by @clue and #455 by @SimonFrings)