Add translations to an enum using a given Gettext backend and domain.

This macro will define a number of functions to display translated enum values to your users:

• show_XXX/1 - shows a translated enum value. Takes the internal value as argument and returns the translated value.

• options_for_XXX/0 - returns a list of pairs of the form {translated_user_visible_string, internal_value}. This list can be fed into Phoenix's and Forage's HTML select widgets.

• non_empty_valid_values_for_XXX/0 - returns a list of internal enum values

• valid_values_for_XXX/0 - returns a list of internal enum values (including the empty string)

TODO: add examples

Translate multiple enums using the given Gettext backend and domain. The same as calling translated_enum/4 multiple times.