Fixes an ExecutionEngineException on Unity3D iOS.

Hi,

I was having an ExecutionEngineException on Unity3D iOS for attempting to JIT compile the Swap method while running with AOT compilation. Since you're only using it with ints, making it non-generic fixes this. I think the fix is non-invasive enough that you might consider it. Another option is simply inlining the method manually.

Other than that, the library is working great, on all of Windows/Mac/iOS/Android.

Thanks,
Nuno