internal/number: fix rounding issues - rounding with large scales - correct interpretation for engineering - default rounding is exact representation - simplify increments Change-Id: I6a4959974069f5e1706e396a836bd6989b93d60d Reviewed-on: https://go-review.googlesource.com/60350 Run-TryBot: Marcel van Lohuizen <mpvl@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Nigel Tao <nigeltao@golang.org>