better gcc and types.h

src/bmp.h

@@ -1,8 +1,8 @@
+#include "types.h"
+
 #ifndef BMP_H
 #define BMP_H
 
-typedef void line_fn(unsigned long y, char *data_buffer);
-
 void bmp_generate(unsigned long width, unsigned long height,
                   unsigned int color_depth, char *file_path,
                   line_fn generate_line);