not define __getinitargs__, bypass the __init__ constructor
completely.  This uses the trick of instantiating an empty dummy class
and then changing inst.__class__ to the real class.  This is done in
two places: once for the INST and once for the OBJ format code.

Also replaced the much outdated long doc string with a short summary
of the module; the information of that doc string is already
incorporated in the library reference manual.