Feature: Simplify usage by supporting new default loop and making Connector optional. (#100 and #101 by @clue)

// old (still supported)
$proxy = new Clue\React\Socks\Client(
    $url,
    new React\Socket\Connector($loop)
);
$server = new Clue\React\Socks\Server($loop);
$server->listen(new React\Socket\Server('127.0.0.1:1080', $loop));

// new (using default loop)
$proxy = new Clue\React\Socks\Client('127.0.0.1:1080');
$socks = new Clue\React\Socks\Server();
$socks->listen(new React\Socket\SocketServer('127.0.0.1:1080'));

Documentation improvements and updated examples. (#98 and #102 by @clue and #99 by @PaulRotmann)

Improve test suite and use GitHub actions for continuous integration (CI). (#97 by @SimonFrings)