[css-ruby] Anonymous Box Generation and White Space Handling Rewritten

Thanks in part to feedback from Kawabata-san, the CSS Ruby Layout
anonymous box generation rules have been rewritten, and now fully
incorporate white space handling.
   http://dev.w3.org/csswg/css-ruby/#box-fixup

The base-annotation pairing rules have also been updated to account
for the special handling of intra-ruby white space, and various
related sections clarified.

Please review and comment on the changes. I hope to publish a new
WD with the updates, to replace the erroneous draft on /TR, soon.

~fantasai