Python feature

Functools gains a new decorator.

`Defaults' allows its caller to placehold non-None defaults; it becomes unnecessary to know the value a place defaults to.

It might be useful in cases where you want the calling signature to look alike for a group of dispatched functions and the added overhead the decorator adds isn't a problem.  But you probably wouldn't want that overhead all the time, so having it as an optional decorator would be good. -Ron Adam