Feature: Support authentication with URL-encoded special characters. (#66 by @clue)

$user = 'he:llo';
$pass = 'p@ss';
$promise = $factory->createClient(
    rawurlencode($user) . ':' . rawurlencode($pass) . '@localhost'
);

Minor documentation improvements and add support / sponsorship info. (#58 by @clue)

Improve test suite and add .gitattributes to exclude dev files from exports. Prepare PHP 8 support, update to PHPUnit 9 and simplify test matrix. (#57 and #59 by @clue and #61 and #65 by @SimonFrings)