channel: object to track channel state.

This object is basically the embodyment of BOLT #2.  Each HTLC already
knows its own state; this moves them between states and keeps them
consistent.

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

type_to_string.h

@@ -22,6 +22,7 @@ union printable_types {
 	const struct channel_id *channel_id;
 	const struct privkey *privkey;
 	const secp256k1_ecdsa_signature *secp256k1_ecdsa_signature;
+	const struct channel *channel;
 	const char *charp_;
 };