damus-c: add bolt11 parser from CLN

We'll need this for our lightning invoice view

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

damus-c/node_id.h

@@ -0,0 +1,38 @@
+/* Encapsulation for pubkeys used as node ids: more compact, more dangerous. */
+#ifndef LIGHTNING_COMMON_NODE_ID_H
+#define LIGHTNING_COMMON_NODE_ID_H
+#include "config.h"
+#include "short_types.h"
+#include "tal.h"
+
+struct node_id {
+    u8 k[33];
+};
+
+static inline bool node_id_eq(const struct node_id *a,
+                  const struct node_id *b)
+{
+    return memcmp(a->k, b->k, sizeof(a->k)) == 0;
+}
+
+/* Is this actually a valid pubkey?  Relatively expensive. */
+//bool node_id_valid(const struct node_id *id);
+
+/* Convert to hex string of SEC1 encoding. */
+char *node_id_to_hexstr(const tal_t *ctx, const struct node_id *id);
+
+/* Convert from hex string of SEC1 encoding: checks validity! */
+bool node_id_from_hexstr(const char *str, size_t slen, struct node_id *id);
+
+/* Compare the keys `a` and `b`. Return <0 if `a`<`b`, 0 if equal and >0 otherwise */
+int node_id_cmp(const struct node_id *a, const struct node_id *b);
+
+/* If the two nodes[] are id1 and id2, which index would id1 be? */
+static inline int node_id_idx(const struct node_id *id1,
+                  const struct node_id *id2)
+{
+    return node_id_cmp(id1, id2) > 0;
+}
+
+/* marshal/unmarshal functions */
+#endif /* LIGHTNING_COMMON_NODE_ID_H */