Don't silently drop data when trying to send on a closed connection

[SeanTAllen]

Currently send on a TCPConnectionActor looks like:

  fun ref send(data: ByteSeq) =>
    if self().state is Open then
      try
        PonyTCP.send(self().event, data, data.size())?
    end

If the connection is closed, or there is otherwise an error, that is silently eaten. Ideally what is needed here is some sort of return that allows a caller to know if there was success or not. Then, you could write a behavior like:

be send(sender: SuccessCallbackHaver, data: ByteSeq) =>
  if not send(data) then
    sender.failure()
  end

to indicate the lack of success.

[SeanTAllen]

send is now a function in TCPConnection