delete() for all structures.

lib/stack.c

@@ -11,12 +11,18 @@ void allocate_stack(struct stack **stack) {
 }
 
 void initialize_stack(struct stack *stack) {
-  stack->card = NULL;
   stack->next = NULL;
 
   return;
 }
 
+void delete_stack(struct stack *stack) {
+  delete_card(stack->card);
+  free(stack);
+
+  return;
+}
+
 bool empty(struct stack *stack) {
   return(stack->card == NULL);
 }