Add meta-files, board structure, and alloc function

Adds meta-files such as the Makefile and flake.lock/nix for easier
project management.

Adds board structure in connect4.h, as well as some helper functions
such as the make_board function to create a board, and the print_board
function to view the board after creation.

flake.nix

@@ -0,0 +1,28 @@
+{
+  description = "C Development";
+
+  inputs = {
+    nixpkgs.url = "nixpkgs/nixos-unstable";
+  };
+
+  outputs = { self, nixpkgs }:
+  let
+    system = "x86_64-linux";
+    pkgs = nixpkgs.legacyPackages.${system};
+    libs = with pkgs; [
+      git
+      gnumake
+      gcc
+      gdb
+      # clang_16
+      # clang-tools_16
+      # lld_16
+      # llvmPackages_16.libllvm
+    ];
+  in {
+    devShells.${system}.default = pkgs.mkShell {
+      buildInputs = libs;
+      LD_LIBRARY_PATH = pkgs.lib.makeLibraryPath libs;
+    };
+  };
+}