Add file upload resource

#56

![postman-3](https://cloud.githubusercontent.com/assets/125707/3352672/5d168a64-fa54-11e3-9d0f-172489852b02.jpg)

Maybe we can do this instead to have return type consistency:

```php
return variable_get('restful_file_upload_allow_anonymous_user', FALSE) || !!$user->uid;
```