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/hash_u5.h

@@ -0,0 +1,20 @@
+/* bech32 (thus bolt11) deal in 5-bit values */
+#ifndef LIGHTNING_COMMON_HASH_U5_H
+#define LIGHTNING_COMMON_HASH_U5_H
+#include "sha256.h"
+#include "short_types.h"
+
+/* Type to annotate a 5 bit value. */
+typedef unsigned char u5;
+
+struct hash_u5 {
+    u64 buf;
+        unsigned int num_bits;
+        struct sha256_ctx hash;
+};
+
+void hash_u5_init(struct hash_u5 *hu5, const char *hrp);
+void hash_u5(struct hash_u5 *hu5, const u5 *u5, size_t len);
+void hash_u5_done(struct hash_u5 *hu5, struct sha256 *res);
+
+#endif /* LIGHTNING_COMMON_HASH_U5_H */