internal/number: scientific encoding Implement spec’s suggestion for rendering scientific notation. Added TODO for supporting HTML variant. Change-Id: I05b263f598cec44ad1670c8d74196c3a8745a211 Reviewed-on: https://go-review.googlesource.com/46251 Run-TryBot: Marcel van Lohuizen <mpvl@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Nigel Tao <nigeltao@golang.org>