[Proposal] Weak reference implementation for D

[Robert]

>        * Robert's one from his new `std.signals` implementation proposal:
>  
> https://github.com/phobos-x/phobosx/blob/d0cc6b45511465ef1d493b0d7226ccb990ae84e8/source/phobosx/signal.d
> 

Obviously I don't see it, otherwise I would have fixed it. Maybe you
could elaborate a bit on your claim? Your implementation uses an
entirely different technique for hiding the reference so a direct
comparison is quite hard.

Best regards,

Robert