Allowing nested loops over lists

Faux mustache functionality, like:

-- content: ---
{{#items}}
Name: {{name}}
Count: {{count}}
{{/items}}

-- args: --
$args = [
  'items' => [
    ['name' => 'John Doe', 'count' => 5],
    ['name' => 'Jane Doe', 'count' => 7],
  ],
];