Updated build instructions; Maven 3.0.3+ is not required; upgraded Clover plugin to 3.1.10

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpcore/trunk@1433699 13f79535-47bb-0310-9956-ffa450edef68
Fixed style check violations (tabs introduced by a previous commit)

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpcore/trunk@1433704 13f79535-47bb-0310-9956-ffa450edef68