def add_change(address, metadata={})
      add_output(
        value: change_value,
        address: address,
        metadata: {memo: "change"}.merge(metadata)
      )
    end
def add_change(address, metadata={})
      add_output(
        value: change_value,
        address: address,
        metadata: {memo: "change"}.merge(metadata)
      )
    end
Add an output to receive change for this transaction.
 Takes a bitcoin address and optional metadata Hash.