In this release, the default `HttpClient` returns *cancelable* futures.

The default `HttpClient` is created by a call to `HttpClient.newHttpClient()`, or by invoking the `build` method on builders returned by `HttpClient.newBuilder()`.
The implementation of the `sendAsync` methods in the default `HttpClient` now return `CompletableFuture` objects that are *cancelable*.
Invoking `cancel(true)` on a *cancelable* future that is not completed, attempts to cancel the HTTP exchange in an effort to release underlying resources as soon as possible. More information can be obtained by reading the API documentation of the `HttpClient::sendAsync` methods.