Add a seg fault handler on Windows

[mkilgore]

#566 adds a SIGSEGV handler for Linux and Mac OS that attempts to log an error before exiting. This is a pretty nice feature as it can allow you to get a stacktrace when a seg fault happens (or at least, attempt to get one, there's no guarantee things are in a state to successfully capture one). I have not tried adding a SIGSEGV handler on Windows but I don't think it works, it looks like SetUnhandledExceptionFilter is the way to do this on Windows.

A big catch here is that I'm not sure that SetUnhandledExceptionFilter is called from the thread that triggered the seg fault. If not then it might get messy as I'm not sure _Unwind_Backtrace offers a way to do a stacktrace from a separate stack-pointer.