Noticed that I had forgot to include NiObject.cpp in my last commit... unfortunately I've already started splitting off classes into their own files so that's included in this commit as well.
I also noticed that I never implemented the member functions of Ref!  I still haven't, but I was just surprised it's been compiling without complaint.

Got rid of globals for good measure.

Moved things around and updated xml_extract.h so that everything compiles again.  Other than NIF_Blocks.h/cpp which will be removed in the future, of course.

Implemented some of the object hierarchy the new way in nif_objects.h and started updating niflib.cpp.

Removed interfaces and moved documentation to real classes.  NIF_Blocks.cpp and niflib.cpp no longer compile.