Made res available in user.use(req, res)

Hello,

This is an update to make ```res``` available in ```user.use(req, res)```. My use case creates a ```res.jsonAuthorized``` method that filters the response, using a JSON Schema, before calling ```res.json```:

```javascript
var filter = require('json-schema-filter');
var fs = require('fs');
var highland = require('highland');
var moderatorAuthorizationSchema = require('./authorization-schemas/moderator.json');

user.use('access private page', function (req, res) {
  if (req.user.role === 'moderator') {
    var moderatorFilter = highland.curry(filter, moderatorAuthorizationSchema);
    res.jsonAuthorized = highland.compose(res.json, moderatorFilter);
    return true;
  }
});
```