Archive extraction support for rackspace cloud files

```
client.extract({
   format: "tar.gz"//by default,
   local: "",//file path
   stream: ""//readable stream
}, function(e,success, resp) {
})
```

See more at http://docs.rackspace.com/files/api/v1/cf-devguide/content/Extract_Archive-d1e2338.html