Breaking changes

• The close status code is now set to 1005 if the received close frame contains
  no status code (a31b1f6).
• Error messages and types have been updated (695c5ea).
• The onerror event handler now receives an ErrorEvent instead of JavaScript
  error (63e275e).
• The third argument of WebSocket.prototype.ping() and
  WebSocket.prototype.pong() is no longer a boolean but an optional callback
  (30c9f71).
• The non-standard protocolVersion and bytesReceived attributes have been
  removed (30c9f71...ee9b5f3).
• The extensions attribute is no longer an object but a string representing
  the extensions selected by the server (fdec524).
• The 'headers' event on the client has been renamed to 'upgrade'. Listeners
  of this event now receive only the response argument (1c783c2).
• The WebSocket.prototype.pause() and WebSocket.prototype.resume() methods
  have been removed to prevent the user from interfering with the state of the
  underlying net.Socket stream (a206e98).