Added header guard

libduck/libduck.h

+#ifndef _LIBDUCK_H
+#define _LIBDUCK_H
+
 #define MOTOR_1 1
 #define MOTOR_2 2
 #define MOTOR_3 3
@@ -12,3 +15,5 @@ int duck_set_position(int motor, int angle);
 int duck_delay(int ms);
 int duck_set_velocity(int motor, int deg_per_sec);
 void close_duck(void);
+
+#endif /* _LIBDUCK_H */