Repository Commits Get All

Added the logic for getting all commits for a repository including unit
tests and XML docs

Octokit/Clients/IRepositoryCommitsClient.cs

@@ -1,4 +1,5 @@
-using System.Diagnostics.CodeAnalysis;
+using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Threading.Tasks;
 
 namespace Octokit
@@ -15,5 +16,13 @@ namespace Octokit
         /// <returns></returns>
         [SuppressMessage("Microsoft.Naming", "CA1716:IdentifiersShouldNotMatchKeywords", MessageId = "base")]
         Task<CompareResult> Compare(string owner, string name, string @base, string head);
+
+        /// <summary>
+        /// Gets all commits for a given repository
+        /// </summary>
+        /// <param name="owner">The owner of the repository</param>
+        /// <param name="name">The name of the repository</param>
+        /// <returns></returns>
+        Task<IReadOnlyList<GitHubCommit>> GetAll(string owner, string name);
     }
 }