code: def to_s
        [
          Hexnum.new(@id, 4).to_s,
          @date.utc.iso8601,
          Hexnum.new(@amount.to_i, 16),
          @prefix,
          @bnf,
          @details,
          @sign
        ].join(';')
      end
docs: Make a new object of this class (you must read the White Paper
   in order to understand this class).
  
   +id+:: is the ID of the transaction, an integer
   +date+:: is the date/time of the transaction
   +amount+:: is the amount, an instance of class +Amount+
   +prefix+:: is the prefix from the Invoice (read the WP)
   +bnf+:: is the wallet ID of the paying or receiving wallet
   +details+:: is the details, in plain text