Enable AMQP over SSL, topic exchanges, and graphite format

This is a pretty significant change :fire: to the current statsd/amqp implementation.

I've outlined the changes below:

* Messages are sent to an AMQP topic exchange instead of a queue
* Exchanges _must_ be `topic` and set to `durable`
* Messages can be sent in JSON format, or in Graphite format (`metric value timestamp\n`)
* JSON messages use the `json_payload` routing key
* GRAPHITE messages use the metric namespace as routing key
* Graphite metric namespacing are using the new format, not the legacy format [See Namespacing doc](https://github.com/etsy/statsd/blob/master/docs/namespacing.md)
* Namespacing, except for `prefixStats` is not configurable (yet)
* The previous `node-amqp` library was inadequate and extremely buggy, it was replaced with `amqplib`
* It is now possible to have encrypted AMQP connections by specifying the proper SSL keys and certificate files
* There is no support for sets or histograms (yet)
* Tested and works with **RabbitMQ**