Organize classes better

Closes #94

Octokit/Models/Response/ApiError.cs

@@ -0,0 +1,26 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
+
+namespace Octokit
+{
+#if !NETFX_CORE
+    [Serializable]
+#endif
+    public class ApiError
+    {
+        /// <summary>
+        /// The error message
+        /// </summary>
+        public string Message { get; set; }
+
+        /// <summary>
+        /// URL to the documentation for this error.
+        /// </summary>
+        public string DocumentationUrl { get; set; }
+
+        // TODO: This ought to be an IReadOnlyList<ApiErrorDetail> but we need to add support to SimpleJson for that.
+        [SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
+        public IList<ApiErrorDetail> Errors { get; set; }
+    }
+}