Numeric (and accumulators)

[Brian Goetz]

>> But there's a much better move here -- take the opportunity to provide
>> standardized forms of structured accumulators. ...
>>
>> All of these might live in package java.util.functions?
>
> After fleshing out a bit, I'm now thinking that a variant of
> this would be better in j.u.c as a refactoring of
> jsr166e.LongAdder etc. The availability of non-thread-safe forms
> as well would then just be an opportunistic byproduct.

Yes, I had a note to write up why I thought this was a better strategy, 
but you beat me to it.

My intent is that j.u.f is really just for SAM types and their minimal 
helper methods (e.g., Predicate.and).