Add a type parameter to theme_links

<menu> has made a comeback in HTML5, we can use menu to build menubar/toolbar type menus.

theme_links seems like a reasonable function to use to build a menubar (e.g. toolbar module uses theme_links), however its hard coded to use <ul>, so in the interest of flexibility I propose we could add a type parameter to theme_links e.g.

$type = $variables['type'];
...
$output .= "<$type" . drupal_attributes($attributes) . '>';
...
$output .= "</$type>";

http://api.drupal.org/api/drupal/includes--theme.inc/function/theme_links/8

Tangentially related issue: #1190210: Convert toolbar.tpl.php to HTML5 →