Support Expanding @ModelAttribute Request Params

Spring controller request params that are marked with @ModelAttribute
will now be flattened. In other words, instead of generating an
operation model that contains a complex object in the request, the
operation model will
appear to have been defined as accepting individual
simple type request parameters.

Using the @ModelAttribute on a controller method param
declares that Spring should bind request parameters to
the model object. As such, the Swagger model should
really show individual parameters, and not a complex
object type.
I'd be curious what would happen if we had a method like so

```java
public void methodWithModelAttributeAndRequestParam(@ModelAttribute Example example, 
    @RequestParam String foo /*a param with a name that matches a model property*/) {
}
```

I think it should we would want the foo parameter to be merged with the parameters from Example. IOW be a set