How do you theme stuff in Drupal 8? In 7, for example, if you had some data items you could call item_list, via the theme function, pass in a render array and get your markup back.
This is a great resource for those interested: Render API, but no examples that I can see.
How do I do this in Drupal 8? For example, how do I theme an image? Sure, I can probably construct my render array, but does it then have to go off to a twig template or something. Are there any examples yet?