Establish an automatic module name

[dmlloyd]

When used in a modular downstream, it is necessary for each artifact to have a stable module name. Please add an automatic module name to this project. I would suggest that it be org.codehaus.plexus.util.xml or perhaps org.codehaus.plexus.util.xml.pull, based on the top-level package name in the project.

The automatic module name is established by way of the Automatic-Module-Name property in the main section of the artifact manifest.

See also codehaus-plexus/plexus-utils#311.