Split Niflib and Niflib for Python into separate solution files to make explaining how to build them easier.

Made DLL creation optional and added a "Release - DLL" configuration.  The Release configuration creates a static library.

Made all include paths relative so you don't have to set any directories to compile.  Hopefully Amorilia will fix this in the code generation script.
Implemented a few more functions.

Changed projects to use Multi-Threaded DLL code generation rather than Single-Threaded.  This should be more compatible with MSVC++ Express Edition.