Added javadocs for connection management APIs; minor tweaks to connection management APIs; added connection management related examples

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpasyncclient/trunk@1528102 13f79535-47bb-0310-9956-ffa450edef68
Fixed broken SSL tunneling setup; added authenticating proxy example

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpasyncclient/trunk@1528103 13f79535-47bb-0310-9956-ffa450edef68