Feature / BC break: Replace depreacted SocketClient with Socket v0.7 and use connect($uri) instead of create($host, $port) (#51 by @clue)

// old
$connector = new React\SocketClient\TcpConnector($loop);
$client = new Client(1080, $connector);
$client->create('google.com', 80)->then(function (Stream $conn) {
    $conn->write("…");
});

// new
$connector = new React\Socket\TcpConnector($loop);
$client = new Client(1080, $connector);
$client->connect('google.com:80')->then(function (ConnectionInterface $conn) {
    $conn->write("…");
});

Improve test suite by adding PHPUnit to require-dev (#50 by @clue)