Not using headers if access_token is defined as a part of the URL.

Hi again! 

I might be way off here, but if we pass on the access_token as a part of the query string, one shouldn't set the headers?

For instance, if I want to send a POST request I would have to do:

```javascript
oauth.api('POST', '/api?access_token=' + someAccessToken, {
  'some': 'object'
});
```

As if I pass it as params I will have the access_token as a part of my post payload, and if restful that should be just the object I'm trying to create?

Any thoughts?