Update config task should respect commented lines

[eksperimental]

This is the diff after running mix recode.update.config

-    # {Recode.Task.Moduledoc, []},
-    # {Recode.Task.Nesting, []},
+    {Recode.Task.Moduledoc, [exclude: ["test/**/*.{ex,exs}", "mix.exs"]]},
+    {Recode.Task.Nesting, []},

I think it should know if the line is commented, and comment the new entry, whether the line was updated and when the line was not.

[NickNeck]

Good point! Thank you.