Async (NIO) request processing support in ClientHttpEngine

It would be great if RestEasy provides another method in ClientHttpEngine interface with async support (similar to what Jersey does with Connector https://jersey.java.net/apidocs/latest/jersey/index.html) by returning a Future.

This would be very useful when integrating with an httpclient that has an async api, e.g., AsyncHttpclient (https://github.com/AsyncHttpClient/async-http-client). AsyncHttpClient has an api to run asynchronously:

Future<Response> response = httpclient.prepareRequest(httprequest).execute();

However, ClientHttpEngine#invoke method returns as Response object which requires to block by calling the future.get() method.