Implement 403 exception handling

This implements exception handling for the various 403 cases based off
of the Octokit.rb implementation.
https://github.com/octokit/octokit.rb/blob/master/lib/octokit/error.rb

Fixes #85

Octokit/Exceptions/AuthorizationException.cs

@@ -1,6 +1,9 @@
 using System;
+using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Net;
 using System.Runtime.Serialization;
+using Octokit.Internal;
 
 namespace Octokit
 {
@@ -10,20 +13,24 @@ namespace Octokit
 #if !NETFX_CORE
     [Serializable]
 #endif
+    [SuppressMessage("Microsoft.Design", "CA1032:ImplementStandardExceptionConstructors",
+        Justification = "These exceptions are specific to the GitHub API and not general purpose exceptions")]
     public class AuthorizationException : ApiException
     {
-        public AuthorizationException()
+        public AuthorizationException() : base(new ApiResponse<object> { StatusCode = HttpStatusCode.Unauthorized })
         {
         }
 
-        public AuthorizationException(string message)
-            : base(message, null, HttpStatusCode.Unauthorized)
+        public AuthorizationException(IResponse response)
+            : this(response, null)
         {
         }
 
-        public AuthorizationException(string message, Exception innerException)
-            : base(message, innerException, HttpStatusCode.Unauthorized)
+        public AuthorizationException(IResponse response, Exception innerException)
+            : base(response, innerException)
         {
+            Debug.Assert(response != null && response.StatusCode == HttpStatusCode.Unauthorized,
+                "AuthorizationException created with wrong status code");
         }
 
 #if !NETFX_CORE
@@ -33,4 +40,4 @@ namespace Octokit
         }
 #endif
     }
-}
+}