More Robust Handling of Window Resize Events

[zacharygraber]

We are currently checking the size of the window/terminal on launch to make sure there's enough space; however, we should re-check every time the window is resized as well. Resize events are captured by termbox, so this should be simple.

If the user resizes the terminal to be too small, it would likely be best to pause the game and display a message asking them to resize.