mapped Log::error to printf

It is useful for debugging to actually see the error messages.

src/log.h

@@ -25,10 +25,12 @@
 #ifndef _LOG_H
 #define _LOG_H
 
+#include <stdio.h>
 
-#define ERROR1(message)
-#define ERROR2(message, arg1)
-#define ERROR3(message, arg1, arg2)
-#define ERROR4(message, arg1, arg2, arg3)
+
+#define ERROR1(message) printf (message)
+#define ERROR2(message, arg1) printf (message, arg1)
+#define ERROR3(message, arg1, arg2) printf (message, arg1, arg2)
+#define ERROR4(message, arg1, arg2, arg3) printf (message, arg1, arg2, arg3)
 
 #endif /* _LOG_H */