splitting out building of the url object into it's own function

This allows you to grab the url among other things without making the actual request. This is super useful because you can easily make the request yourself and stream it. For example, 

```javascript
var url = yql.buildUrl("SELECT * FROM weather.forecast WHERE (location = 93063)");
request.get(url.href).pipe(process.stdout);
```

Maybe `buildUrl` isn't a great name because it's actually returning an object. Thoughts and/or suggestions?