Feature: Add factory methods for common HTML/JSON/plaintext/XML response types. (#439 by @clue)

$response = React\Http\Response\html("<h1>Hello wörld!</h1>\n");
$response = React\Http\Response\json(['message' => 'Hello wörld!']);
$response = React\Http\Response\plaintext("Hello wörld!\n");
$response = React\Http\Response\xml("<message>Hello wörld!</message>\n");

Feature: Expose all status code constants via Response class. (#432 by @clue)

$response = new React\Http\Message\Response(
    React\Http\Message\Response::STATUS_OK, // 200 OK
    …
);
$response = new React\Http\Message\Response(
    React\Http\Message\Response::STATUS_NOT_FOUND, // 404 Not Found
    …
);

Feature: Full support for PHP 8.1 release. (#433 by @SimonFrings and #434 by @clue)

Feature / Fix: Improve protocol handling for HTTP responses with no body. (#429 and #430 by @clue)

Internal refactoring and internal improvements for handling requests and responses. (#422 by @WyriHaximus and #431 by @clue)

Improve documentation, update proxy examples, include error reporting in examples. (#420, #424, #426, and #427 by @clue)

Update test suite to use default loop. (#438 by @clue)