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.

Removed BoneToMatrix44 helper functions. (They will be implemented in Python in the Blender exporter.)

Added a function to calculate an X-aligned bone matrix from the bone vector and the bone roll, which is convenient to have for the Blender exporter.

Changed Float3, Matrix33, and Matrix44 from C arrays to structures that mimic C arrays ensure accessibility from scripting languages.