Organize classes better

Closes #94

Octokit/Models/Response/ApiErrorDetail.cs

@@ -0,0 +1,18 @@
+using System;
+
+namespace Octokit
+{
+#if !NETFX_CORE
+    [Serializable]
+#endif
+    public class ApiErrorDetail
+    {
+        public string Message { get; set; }
+
+        public string Code { get; set; }
+
+        public string Field { get; set; }
+
+        public string Resource { get; set; }
+    }
+}