v0.4.0

• Feature / BC break: Simplify Collection by extending Response and merging Collector into ActionSender
  (#41 by @clue)

  // old
  $collector = new Collector($client);
  $collector->coreShowChannels()->then(function (Collection $collection) {
      var_dump($collection->getResponse()->getFieldValue('Message'));
  });
  
  // new
  $collector = new ActionSender($client);
  $collector->coreShowChannels()->then(function (Collection $collection) {
      var_dump($collection->getFieldValue('Message'));
  });

• Feature / BC break: Replace deprecated SocketClient with new Socket component and
  improve forward compatibility with upcoming ReactPHP components
  (#39 by @clue)

• Feature / BC break: Consistently require URL when creating client
  (#40 by @clue)