routing: Added IRC announcement glue

Added channel announcement serialization and parsing, as well as the
entrypoints for the IRC peer discovery. Announcements are signed by the
sending endpoint and signatures are verified before adding the channels
to the local view of the topology. We do not yet verify the existence of
the anchor transaction.

utils.c

@@ -7,3 +7,11 @@ char *tal_hexstr(const tal_t *ctx, const void *data, size_t len)
 	hex_encode(data, len, str, hex_str_size(len));
 	return str;
 }
+
+u8 *tal_hexdata(const tal_t *ctx, const void *str, size_t len)
+{
+	u8 *data = tal_arr(ctx, u8, hex_data_size(len));
+	if (!hex_decode(str, len, data, hex_data_size(len)))
+		return NULL;
+	return data;
+}