Document Maven + JDK8 usage

[gboersma]

When running UMLGraph using Maven plugin, errors are generated for the UMLGraph annotations. For the fix, see http://stackoverflow.com/questions/8653128/is-there-any-alternative-for-anotations-and-comments-in-umlgraph second answer on specifying tags in plugin. Add it to documentation.

[tjustel]

I noted that additionalparam tags do not work with the doclet, and maven-javadoc plugin version >= 3.0.0. Use additionalOption instead.

Here is an example of config : https://maven.apache.org/plugins/maven-javadoc-plugin/examples/alternate-doclet.html