Modifications that allow the code to compile under Visual C++ 2013.

Hi Dimitry, I am about to do some stuff with SDL2, and since I'm working with C++, I wanted to give your library a try.

Unfortunately, Microsoft's version of C++ is not fully C++11 compliant, not even with the latest version of Visual Studio (2013).

So, I made some changes that get it to compile; but it's all untested for now. I'm sending you this pull request just in case; I'll completely understand if you decide not to support Visual Studio at all.

Cheers!