[Serializer] Name Converter

| Q                | A
| --------------- | ---
| Doc fix?      | no
| New docs? | yes symfony/symfony#13120
| Applies to   | 2.7

This is the documentation for the Serializer Name Converter feature.
What about the following?

```json
{ "org_name": "Acme Inc.", "org_address": "123 Main Street" }
```