message: Adding memo to transfer type
  also adding readscope to Transaction header
diff: @@ -25,6 +25,7 @@ struct Transaction
  refBlockPrefix UInt32
  expiration Time
  scope AccountName[] # the data may be accessed while processing this transaction
  + readscope AccountName[]
  messages Message[]
  struct SignedTransaction inherits Transaction
  @@ -71,6 +72,7 @@ struct transfer
  from AccountName # may not be the message.sender if message.sender has delegated authority by from
  to AccountName
  amount UInt64
  + memo String
  struct lock
  from AccountName
  