Enhancement: specify generated_dir on devserver startup about appengine-maven-plugin HOT 3 OPEN

It would be better if it somehow tied into the plugin version (and thereby the 
sdk version) and didn't persist during upgrades, or if it provided 
functionality to clean the generated directory without the user manually having 
to delete things.  I would rather this be built in a much different way so it's 
easier for less experienced users of the plugin to take advantage of it.  Let 
me know your thoughts.

Thanks,
Matt

Maybe we could introduce some kind of magic placeholder to generatedDir 
property, something like %{version}, which would be rewritten in runtime with 
plugin version, so that you could specify generatedDir in pom.xml like this:

${user.home}/.appengine/generated/%{version}/${project.artifactId}

We could also add simple goal, appengine:generated_cleanup for example, to 
perform generated directory cleanup.

What do you think?

Is there currently any way to set generated_dir param via maven?