[css3-text-layout] text-combine for Bopomopho case

I noticed text-combine does not support a similar phenomenon that happens with Bopomopho used in Taiwan.

The following is an example. The portion in red is one phrase consisting two words (I heard it means "mouth watering"). While the text goes horizontal, the first word is in Bopomopho laid out vertically in the line height.
http://www.flickr.com/photos/67381643@N00/5069541651/

This is a very similar to tate-chu-yoko (horizontal-in-vertical) in Japanese text layout except it is vertical-in-horizontal.

As the "upright" value is defined as "In horizontal mode this value is equivalent to ‘none’.", which is reasonable, so it would call for a separate value. Considering both cases are upright, the naming of existing value might need to change. One idea is "horizontal" and "vertical", where they mean the composition is always horizontal or vertical.

- kida

# By the way the "Latest version" link is broken. Should it point to http://dev.w3.org/csswg/css3-writing-modes/ ? Also, probably the recommended mail subject prefix should also be updated. Thanks.