Simplify usage by updating to new default loop and making Connector optional

[clue]

This changeset simplifies usage by supporting the new default loop.

// old (still supported)
$proxy = new Clue\React\Socks\Client(
    $url,
    new React\Socket\Connector($loop)
);
$server = new Clue\React\Socks\Server($loop);

// new (using default loop)
$proxy = new Clue\React\Socks\Client('127.0.0.1:1080');
$server = new Clue\React\Socks\Server();

Builds on top of reactphp/event-loop#226, reactphp/event-loop#232, reactphp/socket#260 and reactphp/http#410
Refs clue/reactphp-ssh-proxy#27 and clue/reactphp-http-proxy#41