HTTPCLIENT-1322: Factory method + example for HttpAsyncClientWithFuture. Follow-up to HTTPCLIENT-1307
Contributed by Jilles van Gurp <jilles at jillesvangurp.com>

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpclient/trunk@1462087 13f79535-47bb-0310-9956-ffa450edef68