Demo three: Publish/Subscribe

Using RabbitMQ as a broadcast mechanism. producer.js sends a "log" message to a fanout exchange, and all consumer.js processes will receive log messages.
The producer can only send messages to an exchange. On one side it receives messages from producers and the other side it pushes them to queues.
And what exchange gone do with received message is depend of it's exchange type.
There are a few exchange types available: direct, topic, headers and fanout. For publish/subscribe broadcast demo we gone use fanout.

Running Locally

First start multiple consumers just by running consumer scripts in new terminal windows.
Now in another terminal start producer with following command:
```
node producer.js <arg 1>
```
- <arg 1>: Message you wants to broadcast