Now it reads much more of the index file format, and tries to handle
index1/index2 differences more opaquely. I'm not yet happy with the API, it
needs a bit more work.
This removes the dependency of the Havok SDK or getting the decompiled
skeleton files from TexTools or some other place. Code courtesy of
FFXIVTools. The other two ways of reading skeletons (SKEL and Packfile)
are removed which gets rid of two dependencies.
