Updates Windows binaries and headers for SpiderMonkey 31 and updates binaries for NSPR

Also updates build.sh for some Windows specific workarounds and adds more information about NSPR build to README.txt.
Now builds on Windows with Visual Studio 2010 or later.

Some parts of the code are now a bit uglier because some C++11 features aren't implemented in VS2010 yet and can't be used. Especially these constructors that had to be written manually are quite ugly. I still think it's not a big problem because we can make it less ugly as soon as we decide to drop VS2010 support and it shouldn't be a pain to maintain either.