[MNG-152]  add license and download links

git-svn-id: https://svn.apache.org/repos/asf/maven/doxia/doxia-tools/trunk@1604393 13f79535-47bb-0310-9956-ffa450edef68
improved intro

git-svn-id: https://svn.apache.org/repos/asf/maven/doxia/doxia-tools/trunk@1604397 13f79535-47bb-0310-9956-ffa450edef68
updated parent pom

git-svn-id: https://svn.apache.org/repos/asf/maven/doxia/doxia-tools/trunk@1604398 13f79535-47bb-0310-9956-ffa450edef68