Add spreadsheet program

src/sheet.h

@@ -0,0 +1,20 @@
+#ifndef SHEET_H
+#define SHEET_H
+
+#include <stddef.h>
+#include <string.h>
+#include <stdlib.h>
+#include <err.h>
+#include "config.h"
+
+struct sheet {
+    struct celltree *root_cell;
+    size_t           width;
+    size_t           height;
+    char*            title;
+};
+
+void sheet_init(struct sheet *s, size_t width, size_t height, char* title);
+void sheet_delete(struct sheet *s);
+
+#endif