Branch a 3.0.x snapshot for maintenance release in the 3.0.0 line so that work can start on the 3.1.0 release in trunk.

git-svn-id: https://svn.apache.org/repos/asf/activemq/activemq-cpp/branches/activemq-cpp-3.0.x@789495 13f79535-47bb-0310-9956-ffa450edef68