add include guard for lolwut.h

src/lolwut.h

@@ -34,6 +34,10 @@
 /* This represents a very simple generic canvas in order to draw stuff.
  * It's up to each LOLWUT versions to translate what they draw to the
  * screen, depending on the result to accomplish. */
+
+#ifndef __LOLWUT_H
+#define __LOLWUT_H
+
 typedef struct lwCanvas {
     int width;
     int height;
@@ -47,3 +51,5 @@ void lwDrawPixel(lwCanvas *canvas, int x, int y, int color);
 int lwGetPixel(lwCanvas *canvas, int x, int y);
 void lwDrawLine(lwCanvas *canvas, int x1, int y1, int x2, int y2, int color);
 void lwDrawSquare(lwCanvas *canvas, int x, int y, float size, float angle, int color);
+
+#endif