Add stack_print(stack) function

Addresses #12 (closed)

stack.c

@@ -18,9 +18,13 @@ void stack_peek(stack s, int *value){
 }
 
 void stack_print(const stack s) {
-	printf("          TOP\n--------------------\n");
-	for (int* spot = s.data + s.top; spot >= s.data; --spot) {
-		printf("%8d |  %12d\n", spot - s.data, *spot);
+	if (s.top >= 0) {
+		printf("          TOP\n--------------------\n");
+		for (int* spot = s.data + s.top; spot >= s.data; --spot) {
+			printf("%8d |  %12d\n", spot - s.data, *spot);
+		}
+		printf("--------------------\n          BOTTOM\n");
+	} else {
+		printf("STACK EMPTY\n");
 	}
-	printf("--------------------\n          BOTTOM\n");
 }