Third attempt for SUM

[jmh530 via Digitalmars-d]

On Sunday, 13 November 2016 at 16:56:30 UTC, Ilya Yaroshenko 
wrote:
>
> Yes, KBN should be used instead Kahan when possible (for 
> example Quaternions can not be summed using default KBN 
> implementation).
>
> BTW, i have implemented sumOfLogs [1], it is more precise then 
> everything else.
>
> [1] http://dlang.org/phobos/std_numeric.html#.sumOfLog2s

Can you re-order the examples or something so that the first one 
is an example of how it would be used most commonly? The last one 
looks like it should be first, and then maybe only with 
additional explanation (that these are some rarer cases) should 
the others be there.