This document details all the possible changes that you should investigate when updating
  your project from Doctrine Common 2.0.x to 2.1
  
  ## AnnotationReader changes
  
  The annotation reader was heavily refactored between 2.0 and 2.1-RC1. In theory the operation of the new reader should be backwards compatible, but it has to be setup differently to work that way:
  
      $reader = new \Doctrine\Common\Annotations\AnnotationReader();
      $reader->setDefaultAnnotationNamespace('Doctrine\ORM\Mapping\\');
      // new code necessary starting here
      $reader->setIgnoreNotImportedAnnotations(true);
      $reader->setEnableParsePhpImports(false);
      $reader = new \Doctrine\Common\Annotations\CachedReader(
          new \Doctrine\Common\Annotations\IndexedReader($reader), new ArrayCache()
      );
  
  ## Annotation Base class or @Annotation
  
  Beginning after 2.1-RC2 you have to either extend ``Doctrine\Common\Annotations\Annotation`` or add @Annotation to your annotations class-level docblock, otherwise the class will simply be ignored.
  
  ## Removed methods on AnnotationReader
  
  * AnnotationReader::setAutoloadAnnotations()
  * AnnotationReader::getAutoloadAnnotations()
  * AnnotationReader::isAutoloadAnnotations()
  
  ## AnnotationRegistry
  
  Autoloading through the PHP autoloader is removed from the 2.1 AnnotationReader. Instead you have to use the global AnnotationRegistry for loading purposes:
  
      \Doctrine\Common\Annotations\AnnotationRegistry::registerFile($fileWithAnnotations);
      \Doctrine\Common\Annotations\AnnotationRegistry::registerAutoloadNamespace($namespace, $dirs = null);
      \Doctrine\Common\Annotations\AnnotationRegistry::registerAutoloadNamespaces($namespaces);
      \Doctrine\Common\Annotations\AnnotationRegistry::registerLoader($callable);
  
  The $callable for registering a loader accepts a class as first and only parameter and must try to silently autoload it. On success true has to be returned.
  The registerAutoloadNamespace function registers a PSR-0 compatible silent autoloader for all classes with the given namespace in the given directories.
  If null is passed as directory the include path will be used.