file io

- We still need to come up with a naming metaphor for this!
- it is a pipeline communication to stream a file from a server to a client.
- It follows a model similar to: http://zguide.zeromq.org/c:fileio3
Imagine the beauty if the could would be 
```const auto next = NextChunkId();
   if (next == FileSend::Result::TerminatedConnection)```

   Then you also would not need an explaining comment. The code would be crystal clear.