[css3-text] text-emphasis-position

As the spec says, the preferred value of text-emphasis-position is
language dependent ('above right' for Japanese, 'below right' for
Chinese).

Because of that, I think we should also accept 'auto', and use it as
the default value. When the language is not known, it would do the
same as the current default ('above right'), but if the language is
known, it would switch to the appropriate behavior.

What do you think?

    - Florian