Minimal Connect Four game for The Odin Project

Run with ruby example_game.rb Here's how it looks like:

  - black wins! -
  -             -
  -             -
  -      ■      -
  -    □ ■      -
  -    □ ■      -
  -    □ ■      -
  -1 2 3 4 5 6 7-