removed the harcoded ${maven.build.dir}/generated-src/main/java path and introduced the "maven.gen.src" for consistency with the eclipse plugin.
Fixed documentation and removed unused properties.
git-svn-id: https://svn.apache.org/repos/asf/maven/maven-1/plugins/trunk@327000 13f79535-47bb-0310-9956-ffa450edef68