Updated user's guide.

Realized that Niflib was not compiling in DLL mode, so started working on fixing that.  All NiObject classes need to have NIFLIB_API and NIFLIB_HIDDEN put on each public function, rather than marking the whole class.  Still a lot left to change, but niflib.cpp and ComplexShape.cpp both compile without errors in DLL mode now.

Changed some functions to use pointers instead of Ref templates.
Updated to latest XML description.