[css-ruby-1] Rename ruby-merge: collapse to ruby-merge: merge

[fantasai]

From @r12a

http://www.w3.org/TR/css-ruby-1/#collapsed-ruby
4.2 Sharing Annotation Space: the ruby-merge property

If the ruby-merge property is to remain, i think that a better name for 
the `collapse` value would be `merge`, ie.
ruby-merge: merge;

The meaning of `collapse` is not as obvious as `merge`, to my mind.

This issue is also tracked as Issue 44 in the DoC

[css-meeting-bot]

The CSS Working Group just discussed ruby-merge name, and agreed to the following:

• RESOLVED: rename ruby-merge to merge
• RESOLVED: rename collapse value to merge

The full IRC log of that discussion

<fantasai> Topic: ruby-merge name
<fantasai> https://github.com//issues/5004
<fantasai> github: https://github.com//issues/5004
<dael> fantasai: Rename collapse value of ruby-merge to merge. Can we resolve?
<dael> florian: Not implemented?
<dael> fantasai: Not that I know of
<dael> florian: IN favor
<dael> fantasai: I don't care
<dael> astearns: We can resolve bc no one cares
<fantasai> https://www.w3.org/TR/css-ruby-1/#collapsed-ruby
<dael> astearns: Objections to rename ruby-merge to merge
<fantasai> ruby-merge: separate | collapse | auto
<fantasai> collapse -> merge
<dael> myles: Request that editor adds pictures to this section os spec
<dael> fantasai: Fair
<dael> RESOLVED: rename ruby-merge to merge
<fantasai> s/ruby-merge/collapse
<astearns> RESOLVED: rename collapse value to merge

[r12a]

Thank you.

[r12a]

Changed the labels to bring in synch with #786