Composer+own library project setup

./src - project code (your Vendor\ namespace)
./vendor - Composer-managed dependencies
./composer.json
./composer.lock

./src/classloader.php:
<?php
/** Universal stackable classloader.
*
* @version SVN: $Id$
*/

namespace Vendor;

use SplFileInfo;

spl_autoload_register(function($className)
{
  if(strstr($className, '\\', true) !== __NAMESPACE__)
    return;

  $file = new SplFileInfo(__DIR__ . strtr(strstr("$className.php", '\\'), '\\', '/'));
  $path = $file->getRealPath();
  if(!empty($path))
  {
    include_once $path;
  }
});
?>

./src/init.php:
<?php

// Project
require_once __DIR__ . "/classloader.php";

// Composer
require_once dirname(__DIR__) . "/vendor/autoload.php";

./src/app.php:
<?php

namespace Vendor;

require_once __DIR__ . "/init.php";

// your application code here