Sync heartbeat fields with go-algorand, make TxnHeartbeatFields expli…

…cit pointer type on Transaction.

types/heartbeat.go

@@ -7,21 +7,21 @@ type HeartbeatTxnFields struct {
 	_struct struct{} `codec:",omitempty,omitemptyarray"`
 
 	// HeartbeatAddress is the account this txn is proving onlineness for.
-	HbAddress Address `codec:"hbad"`
+	HbAddress Address `codec:"a"`
 
 	// HbProof is a signature using HeartbeatAddress's partkey, thereby showing it is online.
-	HbProof HeartbeatProof `codec:"hbprf"`
+	HbProof HeartbeatProof `codec:"prf"`
 
 	// The final three fields are included to allow early, concurrent check of
 	// the HbProof.
 
 	// HbSeed must be the block seed for this transaction's firstValid
 	// block. It is the message that must be signed with HbAddress's part key.
-	HbSeed Seed `codec:"hbsd"`
+	HbSeed Seed `codec:"sd"`
 
 	// HbVoteID must match the HbAddress account's current VoteID.
-	HbVoteID OneTimeSignatureVerifier `codec:"hbvid"`
+	HbVoteID OneTimeSignatureVerifier `codec:"vid"`
 
 	// HbKeyDilution must match HbAddress account's current KeyDilution.
-	HbKeyDilution uint64 `codec:"hbkd"`
+	HbKeyDilution uint64 `codec:"kd"`
 }

types/transaction.go

@@ -18,7 +18,11 @@ type Transaction struct {
 	AssetFreezeTxnFields
 	ApplicationFields
 	StateProofTxnFields
-	HeartbeatTxnFields
+
+	// By making HeartbeatTxnFields a pointer we save a ton of space of the
+	// Transaction object. Unlike other txn types, the fields will be
+	// embedded under a named field in the transaction encoding.
+	*HeartbeatTxnFields `codec:"hb"`
 }
 
 // SignedTxn wraps a transaction and a signature. The encoding of this struct