type_to_string: move pretty printing of types from log

It's not just useful for logging.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

type_to_string.h

@@ -0,0 +1,30 @@
+#ifndef LIGHTNING_TYPE_TO_STRING_H
+#define LIGHTNING_TYPE_TO_STRING_H
+#include "config.h"
+#include <ccan/tal/tal.h>
+
+/* This must match the type_to_string_ cases. */
+union printable_types {
+	const struct pubkey *pubkey;
+	const struct sha256_double *sha256_double;
+	const struct sha256 *sha256;
+	const struct rel_locktime *rel_locktime;
+	const struct abs_locktime *abs_locktime;
+	const struct bitcoin_tx *bitcoin_tx;
+	const struct htlc *htlc;
+	const struct rval *rval;
+	const struct channel_state *cstate;
+	const struct channel_oneside *channel_oneside;
+	const struct netaddr *netaddr;
+	const char *charp_;
+};
+
+#define type_to_string(ctx, type, ptr)					\
+	type_to_string_((ctx), stringify(type),				\
+			((void)sizeof((ptr) == (type *)NULL),		\
+			 ((union printable_types)((const type *)ptr))))
+
+char *type_to_string_(const tal_t *ctx, const char *typename,
+		      union printable_types u);
+
+#endif /* LIGHTNING_UTILS_H */