Added support for building with VS2013

This turned out to be quite trivial; the only "hard" part was the C2057 compiler error which is caused by the VLA which apparently does not work with Visual C++ , at least not with 2013...

The way I fixed it is certainly not nice, so feel free to suggest alternative ways (or fix it yourself).

I ran the tests, and they all pass (with VS2013, that is - haven't tested on any other platforms, but I doubt that it would break anything).