Allow getting a tree entry by position

lib/geef/tree.ex

@@ -15,21 +15,26 @@ defrecord Geef.Tree, Record.extract(:geef_object, from: "src/geef_records.hrl")
     end
   end
 
-  def get(tree, path) do
-    case :geef_tree.get(rebind(tree), path) do
-      {:ok, entry} ->
-        {:ok, TreeEntry.new entry}
-      error ->
-        error
-    end
-  end
+  defp maybe_entry({:ok, entry}), do: {:ok, TreeEntry.new entry}
+  defp maybe_entry(error = {:error, _}), do: error
+
+  def get(tree, path), do: :geef_tree.get(rebind(tree), path) |> maybe_entry
+  def nth(tree, pos), do: :geef_tree.nth(rebind(tree), pos) |> maybe_entry
 
 end
 
 defimpl Access, for: Geef.Tree do
+  alias Geef.Tree
+
+  def access(tree, key) when is_number(key) do
+    case Tree.nth(tree, key) do
+      {:ok, entry} -> entry
+      {:error, _} -> nil
+    end
+  end
 
   def access(tree, key) do
-    case Geef.Tree.get(tree, key) do
+    case Tree.get(tree, key) do
       {:ok, entry} -> entry
       {:error, _} -> nil
     end