Use pragma once to improve inclusion of header files

include/code.h

@@ -1,6 +1,8 @@
 #include <iostream>
 #include <fstream>
 #include <string>
+#include "types.h"
+#include "utils.h"
 #include "operations.h"
 #include "memory.h"
 #include "branching.h"

include/types.h

@@ -1,3 +1,5 @@
+#pragma once
+
 enum Segment
 {
     LCL,

include/utils.h

@@ -1,3 +1,5 @@
+#pragma once
+
 #include <iostream>
 #include <random>
 #include <ctime>