Add callback interface for errors

Printing to stderr is not the right answer for a library.

builtin.h

@@ -1,9 +1,10 @@
 #ifndef BUILTIN_H
 #define BUILTIN_H
 
+#include "jq.h"
 #include "bytecode.h"
 #include "compile.h"
 
-int builtins_bind(block*);
+int builtins_bind(jq_state *, block*);
 
 #endif