v0.16

[basiliscos]

• [improvement] significant message throughtput increase for std::thread, boost-asio
  and ev backends (upto 5x times)
• [improvement] extended_error can now access to root reason
• [improvement] delivery plugin in debug mode dumps discovery requests and responses
• [improvement/breaking] more details on fatal error (system_context)
• [example] examples/thread/ping-pong-thread.cpp (new)
• [example] examples/ev/ping-pong-ev-2-threads (new)

---

This discussion was created from the release v0.16.