nostrdb: add supporting files for the bolt11 parser

A lot of this was pulled from core-lightning. Not sure what is actually
needed or not.

Signed-off-by: William Casarin <jb55@jb55.com>

nostrdb/cursor.h

@@ -3,15 +3,13 @@
 #define JB55_CURSOR_H
 
 #include "typedefs.h"
+#include "bolt11/likely.h"
 
 #include <stdio.h>
 #include <ctype.h>
 #include <assert.h>
 #include <string.h>
 
-#define unlikely(x) __builtin_expect((x),0)
-#define likely(x)   __builtin_expect((x),1)
-
 struct cursor {
 	unsigned char *start;
 	unsigned char *p;