Allow binding to multiple routing keys.

Simple patch to allow an array of routing keys to be passed into the queue settings. This allows workers to respond to  selectively respond to multiple topics on a topic exchange. 

E.g.
```ruby
class Processor
  include Sneakers::Worker
  from_queue :log_processor,
             exchange: 'topic_logs',
             exchange_type: 'topic',
             routing_key: ['kern.*', '*.critical']

  def work(msg)
    err = JSON.parse(msg)
    if err["type"] == "error"
      $redis.incr "processor:#{err["error"]}"
    end

    ack!
  end
end
```