Updated building instructions

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpclient/trunk@1518780 13f79535-47bb-0310-9956-ffa450edef68
Cleaned up POM

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpclient/trunk@1518781 13f79535-47bb-0310-9956-ffa450edef68
Updated HttpClient 4.3 release notes

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpclient/trunk@1518783 13f79535-47bb-0310-9956-ffa450edef68