swap out node's querystring lib for visionmedia's

visionmedia's querystring parser handles nested attributes and puts them into a common format (common among node-express, ruby on rails, etc)

```javascript
qs.stringify({ user: { name: 'Tobi', email: 'tobi@learnboost.com' }})
// => user[name]=Tobi&user[email]=tobi%40learnboost.com
```

this makes it much easier to interact with such servers using node-request