Short captions for lists

[jwright6323]

Thanks for working on this extension! I would like to suggest adding a feature to use short captions in the generated list. This is useful if you have long explanations in your figure captions that you want to trim out in the list of figures. In LaTeX this is done like so. It seems like this would require some additional asciidoctor markup, so this might not be trivial to implement.

[Alwinator]

I like your idea a lot! However, unfortunately, paid work is keeping me busy! Maybe you can add the feature and make a pull request? That would be cool.|

It should be not that difficult to implement, you need to pass the short captions and then use them here:

https://github.com/Alwinator/asciidoctor-lists/blob/00e1a54d74d1cd7bdf6a4eef5a2856b54ddfc894/lib/asciidoctor-lists/extensions.rb#L54-L62