Simplify usage by supporting new default loop

[SimonFrings]

This changeset simplifies usage by supporting the new default loop.

// old (still supported)
$client = new Clue\React\Ssdp\Client($loop);

// new (using default loop)
$factory = new Clue\React\Ssdp\Client();

Builds on top of reactphp/event-loop#226, reactphp/event-loop#229 and reactphp/event-loop#232

[clue]

@SimonFrings Thanks for the update, changes LGTM!