Create a mix file so OTP releases will work correctly

Signed-off-by: Tom Wilson <tom.wilson@isobar.com>

mix.exs

@@ -0,0 +1,19 @@
+defmodule QRCode.Mixfile do
+  use Mix.Project
+
+  def project do
+    [app: :qrcode,
+     version: "0.0.1",
+     language: :erlang,
+     deps: deps]
+  end
+
+  def application do
+    [applications: [], mod: {:qrcode, []}]
+  end
+
+  defp deps do
+    [
+    ]
+  end
+end