add the first customize options for the no developers peoples.
=> The developers can use the wordpress filter, example:
add_filter( "rakuten_item_price_color", "my_custom_price_color", 10, 1 );
=> or the developers can use the wordpress hook, example:
add_action('wp_head', 'my_custom_head');
0.0.7
remove $rakuten_translation + rakuten_translation() and use __() function (@garyj, @tobifjellner and @peexy : thank you for your help)
0.0.6
add the function : get_rakuten_item_tpl() + apply_filters