DataChannel support (with fallback)

This commit adds support for the WebRTC DataChannel API.
If available, it sends all chat messages through DataChannel.
If not, it falls back to using the websocket.

Author: jbenet

example/index.html

@@ -120,31 +120,62 @@
         })
       }
 
+
+      var websocketChat = {
+        send: function (message) {
+          rtc._socket.send(message);
+        },
+        recv: function (message) {
+          return message;
+        },
+        event: 'receive_chat_msg',
+      };
+
+      var dataChannelChat = {
+        send: function (message) {
+          for (var connection in rtc.dataChannels) {
+            var channel = rtc.dataChannels[connection];
+            channel.send(message);
+          }
+        },
+        recv:  function (channel, message) {
+          return JSON.parse(message).data;
+        },
+        event: 'data stream data',
+      };
+
       function initChat() {
+        var chat;
+
+        if (rtc.dataChannelSupport) {
+          console.log('initializing data channel chat');
+          chat = dataChannelChat;
+        } else {
+          console.log('initializing websocket chat');
+          chat = websocketChat;
+        }
+
         var input = document.getElementById("chatinput");
         var room = window.location.hash.slice(1);
         var color = "#"+((1<<24)*Math.random()|0).toString(16);
 
         input.addEventListener('keydown', function(event) {
           var key = event.which || event.keyCode;
           if (key === 13) {
-            rtc._socket.send(JSON.stringify({
+            chat.send(JSON.stringify({
               "eventName": "chat_msg",
               "data": {
               "messages": input.value,
               "room": room,
               "color": color
               }
-            }), function(error) {
-              if (error) {
-                console.log(error);
-              }
-            });
+            }));
             addToChat(input.value);
             input.value = "";
           }
         }, false);
-        rtc.on('receive_chat_msg', function(data) {
+        rtc.on(chat.event, function() {
+          data = chat.recv.apply(this, arguments);
           console.log(data.color);
           addToChat(data.messages, data.color.toString(16));
         });