[2.0] DDC-412 - Fixed YAML Driver not allowing multiple lifecycle callbacks per event. Backwards-incompatible change

[2.0] DDC-195 - Refactored Mapping Syntax again to be arrays in all annotations, xml and yaml drivers instead of parsing the fields in the AssociationMapping implementations.

[2.0] DDC-336 DDC-337 - Changed @OrderBy annotation to take a DQL not SQL snippet, restrict it to field names and positional orderings. Changed all test-cases and added a test-case that shows the behaviour for OneToMany JoinedSubclassPersister Managed Entities.

[2.0] DDC-336 - Support specification of an OrderBy SQL snippet in OneToMany and ManyToMany Associations in Annotation, XML and YAML Drivers

[2.0] DDC-271 - Add columnDefinition for Join-Column in Annotation, XML and YAML driver, updated SchemaTool to use Join Column definition instead of using the column's columnDefinition if specified. Refactored MappingDriverTest to allow for feature specific test-cases instead of one large assertion block. Fixed typos in XmlDriver - Updated doctrine-mapping.xsd Schema File

[2.0] Unified xml/yaml driver mapping tests so that there is a stronger enforcement on keeping them synchronized feature-wise.

[2.0] Refined implementation and semantics of the merge and detach operations. General cleanups and API improvements. Added a testcase for detaching/serializing->unserializing->modifying->merging to demonstrate the transparent serialization.