Updated project web site for HttpAsyncClient 4.0-beta4 release

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpasyncclient/trunk@1480335 13f79535-47bb-0310-9956-ffa450edef68
Updated HttpAsyncClient 4.0-beta4 release notes

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpasyncclient/trunk@1480336 13f79535-47bb-0310-9956-ffa450edef68