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
The one comment should maybe be put as doxygen comment
```
/// Send enough data requests to fill pipeline
void FileRecv::REquestChunks```