[maven-release-plugin] prepare release 1.5.6

git-svn-id: https://svn.apache.org/repos/asf/santuario/xml-security-java/branches/1.5.x-fixes@1538955 13f79535-47bb-0310-9956-ffa450edef68
[maven-release-plugin] prepare for next development iteration

git-svn-id: https://svn.apache.org/repos/asf/santuario/xml-security-java/branches/1.5.x-fixes@1538957 13f79535-47bb-0310-9956-ffa450edef68