Allow the generate goal to pull info out of source files

[reckart]

Is your feature request related to a problem? Please describe.
The enhance goal may cause problems in environments with incremental build mechanisms. In the best case, it may schedule a second build - in the worst case infinite builds.

Describe the solution you'd like
The enhance goal picks up information from Java source files and adds it to the Java annotations embedded in the class files. If the generate goal could pick up that information and put it directly into the generated XML descriptors, it might not be necessary at all to use the enhance goal to post-process the class files.

Additional context
See #428