Makefile: Simplify and make POSIX compatible

src/captcha.c

@@ -8,8 +8,9 @@ void makegif(unsigned char im[70*200], unsigned char gif[gifsize], int style);
 #include <fcntl.h>
 #include <string.h>
 #include <time.h>
-#include "font.h"
-#include "colors.h"
+
+#include "./font.h"
+#include "./colors.h"
 
 static int8_t *lt[];
 const int gifsize=17646;