spec: update to experimental BOLTs with secret/total_amount.

Also pulls in a new onion error (mpp_timeout).  We change our
route_step_decode_end() to always return the total_msat and optional
secret.

We check total_amount (to prohibit mpp), but we do nothing with
secret for now other than hand it to the htlc_accepted hook.

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

devtools/onion.c

@@ -72,12 +72,13 @@ static void do_generate(int argc, char **argv,
 			struct amount_msat amt;
 			bool use_tlv = streq(argv[1 + i] + klen, "/tlv");
 
+			/* FIXME: support secret and and total_msat */
 			memset(&scid, i, sizeof(scid));
 			amt.millisatoshis = i; /* Raw: test code */
 			if (i == num_hops - 1)
 				sphinx_add_final_hop(sp, &path[i],
 						     use_tlv,
-						     amt, i);
+						     amt, i, amt, NULL);
 			else
 				sphinx_add_nonfinal_hop(sp, &path[i],
 							use_tlv,