theme_link() has been removed

Summary:

• theme_link has been removed from core in order to improve rendering performance and because it no longer provides any benefits over calling l() directly.
• The attributes '#text' and '#path' have been changed to '#title' and '#href' respectively in order to provide consistent attribute naming throughout the Render API and Form API.
• Themers should replace '#theme' => 'link' with '#type' => 'link' in any render arrays, while also changing '#text' to '#title' and '#path' to '#href'.
• An '#options' attribute can be specified that will be passed to l() (and url() internally within l()) to specify extra options for the link such as query parameters, HTML attributes, etc.
• See #1985470-10: Remove theme_link() for the reasoning behind this change.
• Themers should replace any hook_preprocess_link() implementations with a hook_link_alter() implementation. hook_link_alter() was added in #1922454: Gut l(), fix theme('link'), have a working framework for consistently generated links inside and outside of Twig.

Code example:

Before (D7):

$link_array = array(
  '#theme' => 'link',
  '#text' => 'The text to render inside the <a> tag',
  '#path' => 'http://www.example.com/',
);
drupal_render($link_array);

After (D8):

$link_array = array(
  '#type' => 'link',
  '#title' => 'The text to render inside the <a> tag',
  '#url' => Url::fromUri('http://www.example.com/'),
);
drupal_render($link_array);

For additional examples demonstrating usage of both '#options' and hook_link_alter(), please reference https://drupal.org/node/1819788.