These are set up as Twig functions in a module in the NIJC site. This might be pretty sweet to import as a Radicati Drupal module?

RenderMenu.php

<?php

/**
 * @file
 * Contains \Drupal\custom_blocks_forms\Twig\KintExtension.
 */

namespace Drupal\custom_blocks_forms\Twig;

use Drupal;

/**
 * Provides the Kint debugging function within Twig templates.
 */
class RenderMenu extends \Twig\Extension\AbstractExtension
{

  /**
   * {@inheritdoc}
   */
  public function getName()
  {
    return 'custom_render_menu';
  }

  /**
   * {@inheritdoc}
   */
  public function getFunctions()
  {
    return array(
      new \Twig_SimpleFunction('custom_render_block', array($this, 'custom_render_block'), array(
        'is_safe' => array('html'),
        'needs_environment' => TRUE,
        'needs_context' => TRUE,
      )),
      new \Twig_SimpleFunction('custom_render_menu', array($this, 'custom_render_menu'), array(
        'is_safe' => array('html'),
        'needs_environment' => TRUE,
        'needs_context' => TRUE,
      )),
      new \Twig\TwigFunction('custom_render_region', array($this, 'custom_render_region'), array(
        'is_safe' => array('html'),
        'needs_environment' => TRUE,
        'needs_context' => TRUE,
      )),
    );
  }

  public function custom_render_block(\Twig\Environment $env, array $context, $bid)
  {
    $block = \Drupal\block\Entity\Block::load($bid);
    if (!empty($block)) {
      $render = \Drupal::entityTypeManager()
        ->getViewBuilder('block')
        ->view($block);
      return $render;
    }
  }
  /**
   * Provides function to programmatically render a menu
   *
   * @param String $menu_name
   *   The machine configuration id of the menu to render
   * @thanks: https://www.drupal.org/node/2416715 , http://drupal.stackexchange.com/questions/126477/drupal-8-implement-menu-links-as-plugins-trying-to-build-a-menu-tree, https://www.drupal.org/node/2226481
   */
  public function custom_render_menu(\Twig\Environment $env, array $context, $menu_name)
  {
    $menu_tree = \Drupal::menuTree();

    // Build the typical default set of menu tree parameters.
    $parameters = $menu_tree->getCurrentRouteMenuTreeParameters($menu_name);
    //    kint($parameters);
    // Load the tree based on this set of parameters.
    $tree = $menu_tree->load($menu_name, $parameters);

    // Transform the tree using the manipulators you want.
    $manipulators = array(
      // Only show links that are accessible for the current user.
      array('callable' => 'menu.default_tree_manipulators:checkAccess'),
      // Use the default sorting of menu links.
      array('callable' => 'menu.default_tree_manipulators:generateIndexAndSort'),
    );
    $tree = $menu_tree->transform($tree, $manipulators);

    // Finally, build a renderable array from the transformed tree.
    $menu = $menu_tree->build($tree);
    $menu['#attributes']['class'] = array('inline');
    return render($menu);
  }

  /**
   * Provides functionality to programmatically render regions in Twig templates.
   */
  public function custom_render_region(\Twig\Environment $env, array $context, $region)
  {
    // Load region blocks
    $blocks = \Drupal::entityTypeManager()->getStorage('block')->loadByProperties(array('theme' => \Drupal::config('system.theme')->get('default'), 'region' => $region));

    $build = array();
    if (!empty($blocks)) {
      // Sort ‘em
      uasort($blocks, 'Drupal\block\Entity\Block::sort');

      // Capture viewable blocks and their settings to $build
      foreach ($blocks as $key => $block) {
        if ($block->access('view')) {
          $build[$key] = \Drupal::entityTypeManager()->getViewBuilder('block')->view($block);
        }
      }
    }

    return $build;
  }
}