Key streaming in NIF_IO.
Added xml_extract.cpp to SConstruct.
!! The extracted files are based on a modified XML, with CrossRef and Link implemented as uint, and char implemented as byte.

TODO: implement CrossRef and Link in niflib.h?

Added several NifStream functions and << operators to the built-in types.
The new xml_extract.cpp file now compiles.
Problem areas that must be fixed in the generation script were marked with !!BUG!!

Moved some temporary defines to NIF_IO.h.