[css-ruby] Inlinizing Rules

The CSS Ruby spec has a rule that converts any block-level boxes
inside a ruby structure to inline-level boxes. I also just added
a rule that forces any forced line breaks (newline characters)
inside an annotation to collapse, regardless of 'white-space'.

The goal of these is to simplify the rendering model by making it
impossible for an annotation to contain a forced line break: the
only way it breaks is when breaking in parallel with the base text.

I think this is reasonable (and I honestly have no idea what to do
with a forced line break in a ruby annotation). However, it's
possible other people feel differently, so I'm asking for comments
on this behavior.

~fantasai