Two Dimensional List: Connect Four Game

The purpose of this assignment is to practice building, inspecting, and modifying 2D lists effectively. This often requires nested for-loops, but not always. It involves thinking of the structure like an N x M matrix of labeled spots, each with a row- and column-index. As before, restricting ourselves to the most basic functionalities, and any others that you want, you should implement yourself. Two-dimensional lists aren't conceptually more difficult than single-dimension lists, but in practice the nested loops and more complex traversals and interactions merit some extra practice.