In Smalltalk (and Objective-C) classes are just objects, instances of
class Class. new is just a message given to a class object.
If we want to create constructors, where do we put them?
They can't be part of the collection of messages of instances of
the class, since we don't yet have an instance.
They can't be part of the messages understood by class Class,
since not all classes have the same constructor message.
Where do we put the behavior for individual class instances?