Add a node.js benchmarking test program, to see how fast node can receive messages.

test/compatibility/node/devnull_client.js

@@ -0,0 +1,42 @@
+//
+// With ws@7.3.1
+// and 
+// node --version
+// v13.11.0
+//
+// In a different terminal, start a push server:
+// $ ws push_server -q
+//
+// $ node devnull_client.js
+// messages received per second: 16643
+// messages received per second: 28065
+// messages received per second: 28432
+// messages received per second: 22207
+// messages received per second: 28805
+// messages received per second: 28694
+// messages received per second: 28180
+// messages received per second: 28601
+// messages received per second: 28698
+// messages received per second: 28931
+// messages received per second: 27975
+//
+const WebSocket = require('ws');
+
+const ws = new WebSocket('ws://localhost:8008');
+
+ws.on('open', function open() {
+  ws.send('hello from node');
+});
+
+var receivedMessages = 0;
+
+setInterval(function timeout() {
+  console.log(`messages received per second: ${receivedMessages}`)
+  receivedMessages = 0;
+}, 1000);
+
+ws.on('message', function incoming(data) {
+  receivedMessages += 1;
+});
+
+