[css-ruby] ruby-overhang:none is too agressive

[frivoal]

I suspect that the behavior we specified for ruby-overhang: none is overly aggressive, and that the one alluded to in Simple Ruby is better: instead of forbidding all overhang, it is forbidden except over (ideographic) spaces as well as the blank portion of the various CJK punctuation characters who contain a large blank (、, 。 and the like).

This behavior is clearly a bit more complicated to implement, but I am reasonably sure that if an implementation had both what we currently call none and that, no author would consciously chose the currently specified none.

I propose that we either change the definition of none to become that, or that we at least allow both variants.