Added the ability to create directory structures for the output directory

We want to use the visualee tool and integrate that into our maven build, and have the report as a custom report in out maven site, because it provides us with a useful view on the code. It is running during the "build" lifecycle in maven. We do not want to tie the "build" and the "site" life cycle together - visualee can create a directory for the report, but generating a path under "target/site/visualee" would fail if the path "target/site" does not exist. 
One way of creating that path would be to use anttasks, but we believe that the change her is simple and does not complicate the maven configuration. 

Best Regards Allan