The current context is not stored anymore. Instead, it is passed around the traverser
and the visitors. For this reason, validation can occur in multiple contexts at the
same time.
The validation of values against constraints should be a first-class citizen
in the API. For this reason, validate() now takes a value and a constraint or
a list of constraints. This method should be used for the most basic use
cases.
If users want to annotate objects with constraints (this is optional,
advanced functionality), they can use the more expressive validateObject()
method now. For traversing arrays or Traversables, a new method
validateCollection() is now available in the API.
