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.

connect4.c

@@ -0,0 +1,43 @@
+#include "connect4.h"
+#include <stddef.h>
+#include <stdlib.h>
+#include <stdio.h>
+
+struct Board *make_board(size_t height, size_t width) 
+{
+  struct Board *new_board = malloc(sizeof(*new_board));
+  if (!new_board)
+    return NULL;
+  new_board->tilemap = calloc(height*width, sizeof(*(new_board->tilemap)));
+  if (!new_board->tilemap)
+    goto out_tilemap;
+  new_board->tile_heights = calloc(width, sizeof(*(new_board->tile_heights)));
+  if (!new_board->tile_heights)
+    goto out_tile_heights;
+  
+  new_board->height = height;
+  new_board->width = width;
+  new_board->next_player = RED;
+
+  return new_board;
+
+out_tile_heights:
+  free(new_board->tilemap);
+out_tilemap:
+  free(new_board);
+  return NULL;
+}
+
+int drop_tile(struct Board *board, size_t drop_pos) {
+  return 0;
+}
+
+void print_board(struct Board *board) {
+  for (int j = 0; j < board->height; j++) {
+    for (int i = 0; i < board->width; i++) {
+      printf("%d", IDX(i, j, board));
+    }
+    printf("\n");
+  }
+
+}