Certain macros and typedefs were ending up in Doxygen output
that have no reason to be documented for outside users.
Mostly I used Doxygen conditionals to hide them.
In a couple of cases I had some internal functions that needed
to be declared static so Doxygen hides them.
Added DoxygenLayout.xml, but not using it yet.
Still trying to figure out how to make Markdown output
that doesn't look terrible. Not sure I can get Moxygen
to do what I want. I may have to create my own simple(?) tool.
