v0.4.0

• BC break: The Client class has been renamed to StreamingClient.
  Added new Client interface.
  (#18 and #19)
• BC break: Rename message event to data.
  (#21)
• BC break: The Factory now accepts a LoopInterface as first argument.
  (#22)
• Fix: The close event will be emitted once when invoking the Client::close()
  method or when the underlying stream closes.
  (#20)
• Refactored code, improved testability, extended test suite and better code coverage.
  (#11, #18 and #20)

Note: This is an intermediary release to ease upgrading to the imminent v0.5 release.