functions.php

<?php
error_reporting(E_ALL);
ini_set('display_errors', TRUE);
ini_set('display_startup_errors', TRUE);
require_once __DIR__ . '/vendor/autoload.php';
use Timber\Site;

class StarterSite extends Site {

	function __construct() {
		add_theme_support('post-formats');
		add_theme_support('post-thumbnails');
		add_theme_support('menus');
		add_filter('timber_context', array($this, 'add_to_context'));
		add_filter('get_twig', array($this, 'add_to_twig'));
		add_action('init', array($this, 'register_post_types'));
		add_action('init', array($this, 'register_taxonomies'));
		parent::__construct();
	}

	function register_post_types() {
		//this is where you can register custom post types
	}

	function register_taxonomies() {
		//this is where you can register custom taxonomies
	}

	function add_to_context($context) {
		$context['menu'] = new Timber\Menu();
		$context['site'] = $this;
		return $context;
	}

	function add_to_twig($twig) {
		/* this is where you can add your own fuctions to twig */
		$twig->addExtension(new Twig_Extension_StringLoader());
		/** Example how to add a filter
		$twig->addFilter('myfoo', new Twig_SimpleFilter('myfoo', function(){
                    # some filter code
		}));
		*/
		 /** Example how to add a function
		 $twig->addFunction(new Twig_SimpleFunction($MyTwigFunction',function ($MyArgument1) {
	   	  // some code
	         }));
		 */
		return $twig;
	}

}

new StarterSite();