updated to Doxia base and Doxia Site Tools 1.6

git-svn-id: https://svn.apache.org/repos/asf/maven/plugins/trunk@1607177 13f79535-47bb-0310-9956-ffa450edef68
use maven-reporting-exec 1.2

git-svn-id: https://svn.apache.org/repos/asf/maven/plugins/trunk@1607194 13f79535-47bb-0310-9956-ffa450edef68