Added proxy example, with SSE html page

examples/sse.html

@@ -0,0 +1,21 @@
+<html>
+  <head>
+    <script type="text/javascript">
+    window.onload = function() {
+      var es = new EventSource("/api/sse");
+      var div = document.getElementById('events');
+      es.onmessage = function(ev) {
+        var el = document.createElement('div');
+        el.innerHTML = 'sse message: ' + ev.data;
+        div.appendChild(el);
+        // Keep only last 5 messages in the list
+        while (div.childNodes.length > 5) div.removeChild(div.firstChild);
+      };
+    };
+    </script>
+  </head>
+  <body>
+    <h1>SSE pushes, done by separate threads at random times:</h1>
+    <div id="events"></div>
+  </body>
+</html>