Bind interface

I needed the ability to listen on specific interfaces, seemed like something easy enough to update. Let me know if there's some broken conventions or nitpicky things, this is my first experience with C++ libraries and I'm eager to learn.

I was going to update the tests, but I couldn't think of a meaningful test other than just specifying 127.0.0.1 or a non-0.0.0.0 option to ensure it doesn't fail. Let me know if you want that and I can add it.