title: Doxygen not listing nested namespaces
body: <p>I have updated our c++ class comments to doxygen format and they look nice... but the namespaces list/tab is not at all useful. We have a parent namespace e.g <code>john</code> and then sub-namespaces for each library or functional area e.g <code>john::graphics</code>, <code>john::sound</code>, etc.
  Doxygen is only listing a single namespace: <code>john</code>.
  Do I have to simply change some setting, or is it mandatory to document my namespaces for doxygen to pick them up?</p>