Simplify usage by supporting new default loop

[clue]

This changeset simplifies usage by supporting the new default loop.

// old (still supported)
$browser = new React\Http\Browser($loop);
$server = new React\Http\Server($loop, $handler);

// new (using default loop)
$browser = new React\Http\Browser();
$server = new React\Http\Server($handler);

Builds on top of reactphp/event-loop#226, reactphp/event-loop#229, reactphp/event-loop#232, reactphp/stream#159, reactphp/dns#182 and reactphp/socket#260
Refs #361

[clue]

The first commit updates this to the currently unreleased EventLoop, Stream and Socket components to show how the new default loop can be used in this component (the build should be green). The second commit updates this to the releases that have yet to be tagged. This is expected to fail at the moment and should be green once the releases are tagged and the build is restarted.

This is ready for review. I will restart the build and merge once reviewed and the components are tagged.

[clue]

Restarted build and everyhing's green now that reactphp/event-loop v1.2.0, reactphp/stream v1.2.0 and reactphp/socket v1.8.0 have been released

(I've also applied a minor change to work around an unrelated build error on legacy PHP 5.3)