Document default values of list-valued parameters in goal documentation

[arend-von-reinersdorff]

I noticed that the default value src/main/xsd for the sources parameter of the xjc goal is not documented in the goal documentation. The default value is documented on the example page, but I would find it very helpful to also include it in the goal documentation.

This affects other list-valued parameters as well:

• goal xjc
  • sources
  • xjbExcludeFilters
  • xjbSources
  • xjcSourceExcludeFilters
• goal schemagen
  • schemaSourceExcludeFilters
  • sources
• goal testSchemagen
  • testSchemaSourceExcludeFilters
  • testSources
• goal testXjc
  • testSourceExcludeFilters
  • testSources
  • testXjbExcludeFilters
  • testXjbSources

[lennartj]

The documentation - and examples - need some TLC to better show the details about using the plugin. This is a part of it.