hg: lambda/lambda/jdk: Eliminate Collector.Of{Int,Long,Double}; make {Int,Long,Double}Statistics top-level classes; add .statistics() methods to {Int,Long,DOuble}Stream; add Collectors.to{ILD}Statistics(mapper); add Collectors.reduce(mapper, reducer); eliminate Collectors.mapper forms; more efficient implementation of {ILD}Stream.average

[Brian Goetz]

> Joe and I had an offline discussion and we both like "SummaryStatistics"
> as a name, which is common with ParallelArray.  It better captures the
> summary statistics we're gathering: count/sum/min/max.
>
> The question is open about where to put it.  I am open to suggestions.
> It has no dependency on anything in j.u.stream.

I think java.util seems a better home.

> I am on the fence about sum of squares.

After offline discussion with Doug, I tipped over the fence towards "do 
it."