Reimplemented Google Pub/Sub using their new SDK (#14)

* Updated pubsub dependency to the new version

* Changed GooglePubSubProvider to use the new Google SDK

* Now creates both topic and subscription at the same time so messages don't get lost if producer starts before consumer

* Added ACK deadline config option

* Removed blank line

* Removed extra log message

* Fixed subscription options when creating the topic at the same time

* json_decode now returns objects rather than arrays for consistency with the AMQP provider

* getClient is now private

composer.json

@@ -17,12 +17,12 @@
   },
   "suggest": {
     "php-amqplib/php-amqplib": "Enables using queues in RabbitMQ",
-    "google/apiclient": "Enables using queues in Google PubSub"
+    "google/cloud-pubsub": "Enables using queues in Google Cloud PubSub"
   },
   "require-dev": {
     "phpunit/phpunit": "~4.8.0",
     "php-amqplib/php-amqplib": "~2.6.2",
-    "google/apiclient": "~1.0"
+    "google/cloud-pubsub": "~1.3.0"
   },
   "autoload": {
     "psr-4": {