Implemented initial notification API support.

Fixes issue #119

src/main/java/org/kohsuke/github/GitHub.java

@@ -464,6 +464,13 @@ public class GitHub {
         return new GHContentSearchBuilder(this);
     }
 
+    /**
+     * List all the notifications.
+     */
+    public GHNotificationStream listNotifications() {
+        return new GHNotificationStream(this,"/notifications");
+    }
+
     /**
      * This provides a dump of every public repository, in the order that they were created.
      * @see <a href="https://developer.github.com/v3/repos/#list-all-public-repositories">documentation</a>