syncing niflib with xml (note: Union field missing from BoundingVolume; see niflib hack in docsys/nifxml.py)

Add helper method to ControllerSequence which allows for adding item by name and not with target attached.

Update UpdateTangentSpace to match nifskope and add my algorithm adapted from the Obsidian developers version.

   - Fix issue with exporting Skin data causing missing vertexes in nifskope
   - add helper methods for collision related export.
   - fix crashes when exporting animation

Add helper methods to transform shape and fix some typos.

Add miscellaneous collision support helper methods

It seems that a NIF file with NULL property links is still able to be opened by the game engine, so added tests for this in a few places rather than assuming that all links are not NULL.

Added more NormalizeKeys functions.
Added some other functions to some controllers to expose their data.

Separated reference counting features of NiObject into new RefObject class.  This way they won't be buried in the obj folder.
Started adding NormalizeKeys functions to data objects, interpolators, and controllers that deal with keys.  Not yet finished.

Fixing paths in MatTexCollection.cpp to be relative.

Deleting RagDollDescriptor.cpp and RagDollDescriptor.h so that they can be replaced with versions that don't use a capital R.  Seems someone changed the case of this object in the XML file after it had already been included in Niflib.

Forgot to mention it in a previous commit, but I added some template functions for extracting flags and fields from bitfields to NIF_IO.h.  I just put them through some tests and they appear to work correctly.

Finished new MatTexCollection helper class which makes it possible to manipulate material properties and texture objects with the same classes regardless of the intended NIF version.
Realized that only read was implemented for files with version < 3.3.0.13, so implemented write for those old versions as well.