Feature: Forward compatibility with react/promise 3.
(#39 by @WyriHaximus)

Add .gitattributes to exclude dev files from exports.
(#40 by @reedy)

Improve test suite, update to support PHP 8 and PHPUnit 9.3.
(#41 and #43 by @SimonFrings and #42 by @WyriHaximus)