Make configurations compatible with releases

When creating a release, having functions defined via `fn` or via the
`&fun/arity` syntax, breaks the build.

Addict now requires that the hooks are defined via a tuple that defines
the Module and the target function, e.g.: `{ Module, :function}`.

Thanks to @smpallen99 for the tip!

Closes trenpixster#77

configs.md

@@ -27,7 +27,7 @@ And add it to the configuration:
 
 config :addict,
   (...),
-  post_login: &MyApp.PostLoginAction.log/3
+  post_login: {MyApp.PostLoginAction, :log}
 ```
 
 If you want to take different flows according to the success criteria of the action, you can pattern match the arguments:
@@ -128,7 +128,7 @@ And in your configuration file:
 
 config :addict,
   (...),
-  extra_validation: &MyApp.User.validate/2
+  extra_validation: {MyApp.User, :validate}
 ```
 
 # CSRF Token

lib/addict/controller.ex

@@ -148,7 +148,7 @@ defmodule Addict.AddictController do
 
   defp generate_csrf_token do
     if Addict.Configs.generate_csrf_token != nil do
-      Addict.Configs.generate_csrf_token.()
+      Addict.Helper.exec Addict.Configs.generate_csrf_token, []
     else
       ""
     end

lib/addict/helper.ex

@@ -18,4 +18,24 @@ Addict Helper functions
   def is_logged_in(conn) do
     current_user(conn) != nil
   end
+
+  @doc """
+  Utility helper for executing Config defined functions
+  """
+
+  def exec(nil, _) do
+    nil
+  end
+
+  def exec({mod, func}, args) do
+    :erlang.apply mod, func, args
+  end
+
+  def exec(func, []) do
+    :erlang.apply func, []
+  end
+
+  def exec(func, args) do
+    :erlang.apply func, args
+  end
 end

lib/addict/interactors/register.ex

@@ -11,8 +11,8 @@ defmodule Addict.Interactors.Register do
     extra_validation = configs.extra_validation || fn (a,_) -> a end
 
     {valid, errors} = ValidateUserForRegistration.call(user_params)
-    user_params = InjectHash.call user_params
-    {valid, errors} = extra_validation.({valid, errors}, user_params)
+    user_params     = InjectHash.call user_params
+    {valid, errors} = Addict.Helper.exec extra_validation, [{valid, errors}, user_params]
 
     case {valid, errors} do
        {:ok, _} -> do_register(user_params, configs)