Parse nested queues from .yml

I wanted to use links in .yml like this:
```yaml
production:
  :queues: *default_queue
    - generic_tasks
    - other_generic_tasks
super_worker:
  :queues:
    - extra_tasks
    - *default_queue
```
So super_worker will perform extra_tasks first, but when there is no extra_tasks it'll work as usual worker.
extra_tasks can take very long time and I cant add these queues to default process not to busy all workers.

http://stackoverflow.com/a/4949139/1135874 - seems it's the only way to merge arrays in yaml.

I'll write specs if you like this change.