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>
2 files changed