Support casting from module as string ("Elixir.")

[fabriziosestito]

We are using enum_type in our CQRS event store (no Ecto) where structs are deserliazed from a JSON.
It would be useful to support casting from enum modules that were saved as strings in our event store, i.e. "Elixir.Modules."

We solved by adding something like this to each defenum:

Enum.each(@possible_options, fn {k, _} ->
   def cast(unquote(to_string(k))), do: {:ok, unquote(k)}
end)

Thoughts?