handle noop modes inline

this removes an extra lookup and function call when it isn't needed
ensure that a Member is returned from __new__ on clone

if not, just return the bad value and let the Python code handle it
cleanup getattr handler and remove potential for memory leak if validators cause default value recursion
invoke the post setattr handler in the setattro method
update metaclass

This is a new metaclass implementation which is simpler to reason about
than the old version, since it does not make an attempt to share the
members of the base classes. Each class gets its own cloned copy of the
members.