Organize classes better

Closes #94

Octokit/Helpers/IReadOnlyPagedCollection.cs

@@ -0,0 +1,21 @@
+using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
+using System.Threading.Tasks;
+
+namespace Octokit
+{
+    /// <summary>
+    /// Reflects a collection of data returned from an API that can be paged.
+    /// </summary>
+    /// <typeparam name="T"></typeparam>
+    public interface IReadOnlyPagedCollection<T> : IReadOnlyList<T>
+    {
+        /// <summary>
+        /// Returns the next page of items.
+        /// </summary>
+        /// <returns></returns>
+        [SuppressMessage("Microsoft.Design", "CA1024:UsePropertiesWhereAppropriate",
+            Justification = "Makes a network request")]
+        Task<IReadOnlyPagedCollection<T>> GetNextPage();
+    }
+}