[maven-release-plugin] prepare release 0.21

git-svn-id: https://svn.apache.org/repos/asf/rave/trunk@1463817 13f79535-47bb-0310-9956-ffa450edef68
[maven-release-plugin] prepare for next development iteration

git-svn-id: https://svn.apache.org/repos/asf/rave/trunk@1463819 13f79535-47bb-0310-9956-ffa450edef68