This class reads a classfile from a byte array and pulls out the value of the class annotation
for APIVersion, which can then be retrieved by a call to getVersion().
Hopefully the use of ClassReader in this implementation is not too expensive.
An empty tagging interface that can be used if a java class
want control over the class dict initialization.
When a java class implements this interface, it must also have
a method like:
public static void classDictInit(PyObject dict) { ..