Add method for getting repo archive link

Octokit/Clients/IRepositoryContentsClient.cs

@@ -1,5 +1,6 @@
 using System.Collections.Generic;
 using System.Threading.Tasks;
+using Octokit.Internal;
 
 namespace Octokit
 {
@@ -46,6 +47,32 @@ namespace Octokit
         /// <returns></returns>
         Task<string> GetReadmeHtml(string owner, string name);
 
+        /// <summary>
+        /// This method will return a 302 to a URL to download a tarball or zipball archive for a repository.
+        /// Please make sure your HTTP framework is configured to follow redirects or you will need to use the 
+        /// Location header to make a second GET request.
+        /// Note: For private repositories, these links are temporary and expire quickly.
+        /// </summary>
+        /// <remarks>https://developer.github.com/v3/repos/contents/#get-archive-link</remarks>
+        /// <param name="owner">The owner of the repository</param>
+        /// <param name="name">The name of the repository</param>
+        /// <returns></returns>
+        Task<string> GetArchiveLink(string owner, string name);
+
+        /// <summary>
+        /// This method will return a 302 to a URL to download a tarball or zipball archive for a repository.
+        /// Please make sure your HTTP framework is configured to follow redirects or you will need to use the 
+        /// Location header to make a second GET request.
+        /// Note: For private repositories, these links are temporary and expire quickly.
+        /// </summary>
+        /// <remarks>https://developer.github.com/v3/repos/contents/#get-archive-link</remarks>
+        /// <param name="owner">The owner of the repository</param>
+        /// <param name="name">The name of the repository</param>
+        /// <param name="archiveFormat">The format of the archive. Can be either tarball or zipball</param>
+        /// <param name="reference">A valid Git reference.</param>
+        /// <returns></returns>
+        Task<string> GetArchiveLink(string owner, string name, ArchiveFormat archiveFormat, string reference);
+
         /// <summary>
         /// Creates a commit that creates a new file in a repository.
         /// </summary>
@@ -75,4 +102,14 @@ namespace Octokit
         /// <param name="request">Information about the file to delete</param>
         Task DeleteFile(string owner, string name, string path, DeleteFileRequest request);
     }
+
+    public enum ArchiveFormat
+    {
+        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Naming", "CA1704:IdentifiersShouldBeSpelledCorrectly", MessageId = "Tarball")]
+        [Parameter(Value = "tarball")]
+        Tarball,
+        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Naming", "CA1704:IdentifiersShouldBeSpelledCorrectly", MessageId = "Zipball")]
+        [Parameter(Value = "zipball")]
+        Zipball
+    }
 }