HttpClient HTTP request/response API method design that provides non racy methods when called outside event-loop

[vietj]

Racy code called from a non event-loop/worker context thread

// Racy
Future<Buffer> fut = client
   .request(options)
   .compose(req -> req.send())
   .compose(resp -> resp.body());

Instead one should write

// Not racy
Future<Buffer> fut = client
   .request(options)
   .compose(req -> req.send().compose(resp -> resp.body()));

This PR shows a new non racy API design <T> Future<T> request(..., Function<HttpClientRequest, Future<T>>)

// Not racy
Future<Buffer> fut = client.request(options, req -> req
   .send()
   .compose(resp -> resp.body()));

which provides interesting usability:

// Conversion
Future<JsonObject> fut = client.request(options, req -> req
   .send()
   .compose(resp -> resp.body())
   .map(body -> new JsonObject(body)));

[vietj]

asking for @tsegismont @jponge opinion more than a review

[tsegismont]

IIUC, the proposed API enforces the non racy usage that is required with the current API (by taking the transformation chain as a parameter).

LGTM, 👍