Allow a function to be passed in the messages property

[rxaviers]

On globalizejs/globalize#481, @sompylasar has raised a different use case that requires a custom function to return Globalize messages. So, the goal of this issue make the messages option to either accept the string (as documented above) or a function that passes locale as its first argument. For example:

new globalizePlugin({
    production: options.production, // true: production, false: development
    developmentLocale: "en", // locale to be used for development.
    supportedLocales: [ "en", "es", "zh" ], // locales that should be built support for.
    messages: function( locale ) {
        // Messages in the JSON format for requested locale.
        return getMessagesFor( locale );
    }
    output: "globalize-compiled-[locale].[hash].js" // build output.
});

[joerm]

Question: We're coming across this library for use in an upcoming product; localization is important to us, and I've prototyped using this plugin... but an obvious question from others is whether all localized strings are downloaded at once.

What are your priorities around supporting this repo? I've looked at the codebase and a PR in the short term is a bit unlikely given my other priorities. Is this issue currently being worked on?

[rxaviers]

I'm afraid I didn't understand your question "whether all localized strings are downloaded at once". Could you please explain it? I want to make sure I understand why you need this feature.