Merge pull request #59 from jonwd7/fix/num-uv-sets

Num UV Sets fix.  Merging as I have used this for months in NifSkope without issue.  Handling it as one ushort instead of two bytes is the only correct way due to endianness issues.  Addresses all regressions with Bethesda NIFs as well as maintaining non-Bethesda NIF support.  Closes #51