[2.0][DDC-122][DDC-97][DDC-98][DDC-147] Refactored metadata mapping drivers by removing the useless PRELOAD mode. Introduced ClassMetadataFactory#getAllMetadata. Classloader simplifications. Old classloaders deprecated. New Doctrine\Common\ClassLoader is almost the same as the previous IsolatedClassLoader.

[2.0][DDC-22] Fixed. Also cleaned up association handling. More to come: exception refactorings, proxy simplifications (single proxy class, not two).

[2.0][DDC-48][DDC-47] Refactored cache drivers to allow more control over deleting, added namespacing to cache drivers and implemented clear-cache task

[2.0] Added more missing docblocks. Implemented a double-inclusion listener prevention in EventManager

[2.0] Fixed issues discovered during code coverage report generation. Made all ClassMetadata properties public (good reasons, read the class docblock). Performance improvements.