Added quick start example

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpasyncclient/trunk@1537062 13f79535-47bb-0310-9956-ffa450edef68
Set API baseline to 4.0; added Clirr plugin

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpasyncclient/trunk@1537063 13f79535-47bb-0310-9956-ffa450edef68