Generate a RouteHandler per reactive route

[cescoffier]

Description

At the moment, if you have the following route:

@Route(path="/", produces="application/json")
@Route(path="/foo", produces="text/plain")
public void route(RoutingContext rc) { ...}

We generate a single method handler.
So, during the generation, we can't distinguish if we are producing json or text. By generating multiple methods we can introduce
media-type awareness in the generated bytecode to automatically handle the types. For example we can map objects to json or text automatically.