title: Don't found a class php imported with composer
body: <p>in my project I have imported by composer <code>respect/validator</code>. Now, I have a file (login.php) in a subfolder of subfolder where I need it.
  The Respect/Validation's documentation says write: </p>
  
  <p><code>&lt;?php
   use Respect\Validation\Validator as v;</code></p>
  
  <p>obviously I must require my <code>vendor/autoload.php</code> (autogenerate Composer's file), I do it in index.php of my project in the root. Well, it work for every packages (Slim, twig...) but not for Respect/Validation, I try also with other package into my login.php but it's the same.</p>
  
  <p>the error is: <code>Fatal error: Class 'Respect\Validation\Validator' not found</code></p>
  
  <p>so, i try also to require here the autoload.php and the results:</p>
  
  <p><code>Warning: require_once(vendor/autoload.php): failed to open stream: No such file or directory</code></p>
  
  <p><code>Fatal error: require_once(): Failed opening required 'vendor/autoload.php' (include_path='.;C:\xampp\php\PEAR')</code> </p>
  
  <p>I think that the problem is with autoload.php or with the path. Because I should not need the autoload in login.php or however when I require it, it should not change the error...</p>