add client for holding authentication info

lib/forcex/client.ex

@@ -0,0 +1,29 @@
+defmodule Forcex.Client do
+  defstruct auth: nil, endpoint: "https://login.salesforce.com"
+
+  def new do
+    [:username, :password, :security_token, :client_key, :client_secret]
+    |> Enum.map(&( {&1, get_val_from_env(&1)}))
+    |> Enum.into(%{})
+    |> new
+  end
+  def new(auth), do: %__MODULE__{auth: auth}
+  def new(auth, endpoint) do
+    endpoint = if String.ends_with?("/"), do: endpoint, else: endpoint <> "/"
+    %__MODULE__{auth: auth, endpoint: endpoint}
+  end
+
+  defp get_val_from_env(key) do
+    key
+    |> env_var
+    |> System.get_env
+    |> case do
+      nil ->
+        Application.get_env(:forcex, __MODULE__, [])
+        |> Keyword.get(key)
+      val -> val
+    end
+  end
+
+  defp env_var(key), do: "SALESFORCE_#{key |> to_string |> String.upcase}"
+end