Cleanup Channel/Socket

[rbx]

• [x] get rid of unused interfaces (no deprecation needed, since these are unused (at least not known to us)):

  • [x] get rid of SetSendTimeout/GetSendTimeout/SetReceiveTimeout/GetReceiveTimeout (at least from the general interface). Values set by these FairMQSocket methods are currently used only inside each transport - they are transport details. The actual transfer timeouts are controlled by the user via transfer calls, e.g.: Receive(FairMQMessagePtr& msgVec, const int timeout = 0). It is up to the transport how to implement it these. A general timeout value currently has no meaning in the user-facing API.
  • [x] get rid of GetOption/SetOption and replace with specific API, such as SetLinger/GetLinger. This is less error-prone and more type-safe. Currently these interfaces are only used internally in FairMQDevice for high watermark and kernel transfer size settings.
  • [x] get rid of general GetSocket interface - it returns internal socket representation, which should not be visible from the interface API.

• [x] ~~rename SendAsync/ReceiveAsync to more clear TrySend/TryReceive~~ Remove SendAsync/ReceiveAsync, instead Send/Receive with a timeout of 0 can be used (since these are used, this will require a deprecation warning iteration). This is already the case in the transport API, but not yet in Channel API.

• [x] move Bind/Connect/Attach implementations from device class to channel class.

• [ ] introduce (experimental?) value-based move-only fair::mq::Message in parallel to existing FairMQMessage. As a consequence this will require new overloads for send/receive and serialization APIs.

Anything else?