send can fail silently when sending would block (EWOULDBLOCK return for send) (#18)

* try to use a pipe for communication

* flush send buffer on the background thread

* cleanup

* linux fix / linux still use event fd for now

* cleanup

ixwebsocket/IXWebSocket.h

@@ -112,6 +112,7 @@ namespace ix
         const std::string& getUrl() const;
         const WebSocketPerMessageDeflateOptions& getPerMessageDeflateOptions() const;
         int getHeartBeatPeriod() const;
+        size_t bufferedAmount() const;
 
         void enableAutomaticReconnection();
         void disableAutomaticReconnection();