added constants and method to check combine.self value

git-svn-id: https://svn.apache.org/repos/asf/maven/doxia/doxia-sitetools/trunk@1604386 13f79535-47bb-0310-9956-ffa450edef68
[MNG-152]  add license and download links

git-svn-id: https://svn.apache.org/repos/asf/maven/doxia/doxia-sitetools/trunk@1604389 13f79535-47bb-0310-9956-ffa450edef68