[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.
In fact, this will only work if the custom serializer extends the `abstract` class. It will not work if it directly implements the interface, so "any" isn't true.