The https://github.com/nsf/termbox-go library is no longer maintained
so this change replaces it with the maintained
github.com/gdamore/tcell library which has a termbox backwards
compatibility layer.
There are a few minor changes from the termbox library:
- Using Clear with fg bg ColorDefault resulted in a white background for some reason.
- Clear with fg ColorWhite bg ColorBlack was used instead.
- tcell's termbox wrapper doesn't support ColorLightYellow.
- ColorYellow + 8 was used instead.
