restructure into src/

.gitignore

@@ -0,0 +1 @@
+out/

src/mandelbrot.c

@@ -37,7 +37,7 @@ int main() {
       img[i * WIDTH + j] = color_map(depth);
     }
   }
-  write_ppm("mandelbrot.c.ppm", img);
+  write_ppm("out/c.ppm", img);
 
   return 1;
 }