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/bolt11/error.c

@@ -0,0 +1,34 @@
+
+#include "error.h"
+
+#include <stdlib.h>
+#include <stdarg.h>
+
+int note_error_(struct errors *errs_, struct cursor *p, const char *fmt, ...)
+{
+	static char buf[512];
+	struct error err;
+	struct cursor *errs;
+	va_list ap;
+
+	errs = &errs_->cur;
+
+	if (errs_->enabled == 0)
+		return 0;
+
+	va_start(ap, fmt);
+	vsprintf(buf, fmt, ap);
+	va_end(ap);
+
+	err.msg = buf;
+	err.pos = p ? (int)(p->p - p->start) : 0;
+
+	if (!cursor_push_error(errs, &err)) {
+		fprintf(stderr, "arena OOM when recording error, ");
+		fprintf(stderr, "errs->p at %ld, remaining %ld, strlen %ld\n",
+				errs->p - errs->start, errs->end - errs->p, strlen(buf));
+	}
+
+	return 0;
+}
+