fix Geef.Signature for Elixir use

lib/geef/signature.ex

@@ -10,8 +10,12 @@ defmodule Geef.Signature do
   defp maybe_sig({:ok, sig}), do: from_record(sig)
   defp maybe_sig(error = {:error, _}), do: error
 
-  def from_record({:geef_signature}) do
-    %Geef.Signature{}
+  def from_record({:geef_signature, name, email, time}) do
+    %Geef.Signature{name: name, email: email, time: time}
+  end
+
+	def to_record(%Geef.Signature{name: name, email: email, time: time}) do
+    {:geef_signature, name, email, time}
   end
 
 end