HTTPCORE-300: ContentType to provide support for custom parameters

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpcore/trunk@1478742 13f79535-47bb-0310-9956-ffa450edef68
Updated project web site for HttpCore 4.3-beta2 release

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpcore/trunk@1478749 13f79535-47bb-0310-9956-ffa450edef68
Updated HttpCore 4.3-beta2 release notes

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpcore/trunk@1478750 13f79535-47bb-0310-9956-ffa450edef68