code: func HashMerkleBranches(left *chainhash.Hash, right *chainhash.Hash) *chainhash.Hash {
  	// Concatenate the left and right nodes.
  	var hash [chainhash.HashSize * 2]byte
  	copy(hash[:chainhash.HashSize], left[:])
  	copy(hash[chainhash.HashSize:], right[:])
  
  	newHash := chainhash.DoubleHashH(hash[:])
  	return &newHash
  }
docs: // HashMerkleBranches takes two hashes, treated as the left and right tree
  // nodes, and returns the hash of their concatenation.  This is a helper
  // function used to aid in the generation of a merkle tree.