Feature: Forward compatibility with react/promise v3. (#153 by @WyriHaximus)

Feature: Support parsing OPT records (EDNS0). (#157 by @clue)

Fix: Avoid PHP warnings due to lack of args in exception trace on PHP 7.4. (#160 by @clue)

Improve test suite and add .gitattributes to exclude dev files from exports. Run tests on PHPUnit 9 and PHP 7.4 and clean up test suite. (#154 by @reedy, #156 by @clue and #163 by @SimonFrings)