gson deserialization with resource method with many params (json without root)

Gson deserialization doesn't support resource methods with more than one param.

But in some cases, we can have other params that are filled by url params.

e.g:
```java
@Post("/templates/{idTemplate}/data")
public void add(Data data, String idTemplate) {
..
}
```

The `Data` param will be deserialized from json(without root) and `idTemplate` will be filled by url placeholder.