slack-commands.php

class autoloader {

    public static $loader;

    public static function init()
    {
        if (self::$loader == NULL)
            self::$loader = new self();

        return self::$loader;
    }

    public function __construct()
    {
        spl_autoload_register( array($this,'commands') );
    }

    public function commands( $class ) {
        include plugin_dir_path( __FILE__ ) . 'commands/' . $class . '.command.php';
    }

}

//call
autoloader::init();