How to display fullsize image + link on show.php in 2.0?

<?php

$files = $item->Files;
$firstFile = $files[0];

echo display_file($firstFile,array('imageSize'=>'fullsize'));
?>

This bit of code is how to do it in Omeka 1.0-- How do I display the first full-size derivative for an item (sized with css) that links to itself (for a fancy-box effect) on the show items page?

Mostly the same, just a different function:

echo file_markup($file, array('imageSize'=>'fullsize'));

There's a list of function changes here