functions.php

<?php
// Various clean up functions
require_once('library/cleanup.php');

// Required for Foundation to work properly
require_once('library/foundation.php');

// Register all navigation menus
require_once('library/navigation.php');

// Add menu walker
require_once('library/menu-walker.php');

// Create widget areas in sidebar and footer
require_once('library/widget-areas.php');

// Return entry meta information for posts
require_once('library/entry-meta.php');

// Enqueue scripts
require_once('library/enqueue-scripts.php');

// Add theme support
require_once('library/theme-support.php');

if (!class_exists('Timber')){
    add_action( 'admin_notices', function(){
        echo '<div class="error"><p>Timber not activated. Make sure you activate the plugin in <a href="' . admin_url('plugins.php#timber') . '">' . admin_url('plugins.php') . '</a></p></div>';
    });
    return;
}

class StarterSite extends TimberSite {

    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['foo'] = 'bar';
        $context['stuff'] = 'I am a value set in your functions.php file';
        $context['notes'] = 'These values are available everytime you call Timber::get_context();';
        $context['menu'] = new TimberMenu();
        $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());
        $twig->addFilter('myfoo', new Twig_Filter_Function('myfoo'));
        return $twig;
    }

}

new StarterSite();

function myfoo($text){
    $text .= ' bar!';
    return $text;
}