[Validator] Wrapped collections into CollectionNode instances
[Validator] Made traversal of Traversables consistent

If the traversal strategy is IMPLICIT (the default), the validator will now
traverse any object that implements \Traversable and any array
[Validator] Merged validate(), validateObject() and validateObjects() to simplify usage
[Validator] Improved visitor names
[Validator] Removed unused use statements
[Validator] Fixed typos
[Validator] Removed helper class Traversal
[Validator] Fixed tests under PHP<5.3.9

The new implementation is disabled on those PHP versions.
[Validator] Removed unused use statement
[Validator] Fixed the new validator API under PHP < 5.3.9
[Validator] Added deprecation notes
[Validator] Updated outdated doc blocks
[Validator] Completed inline documentation of the Node classes and the NodeTraverser
[Validator] Improved test coverage of NonRecursiveNodeTraverser
[Validator] Improved test coverage and prevented duplicate validation of constraints
[Validator] Visitors may now abort the traversal by returning false from beforeTraversal()
[Validator] Added inline documentation for the PropertyPath utility class
[Validator] Improved inline documentation of the validators
[Validator] Improved inline documentation of CascadingStrategy and TraversalStrategy
[Validator] Improved test coverage of the Traverse constraint