doxygen: avoid most internals

doxygen: avoid most internals

For some reason, all the interals are documented by default.
This is wrong for two basic reasons:

 - We need to focus on public interfaces, since those are
   the architectural interfaces and relationships.

 - Since virtually nothing has doxygen support yet, this
   maximizes the noise, and minimizes the usefulness of
   doxygen output.

So don't expose so much by default.