Issue #22 - Update jetty-maven-plugin for basedir / project.version

+ Renamed all ${basedir} to ${project.basedir} to reflect
  recommendations by the Apache Maven project.
+ Using "${" vs "&#36;{" now that property expansion is fixed.
+ Using @project.version@ for top level XML snippet as that
  one line should be expanded for the specific version of
  jetty the documentation is being built for.