[csswg-drafts] Pull Request: Values copyedit

Crissov has just submitted a new pull request for 
https://github.com/w3c/csswg-drafts:

== Values copyedit ==
This is the trimmed down version of #848. It just adds `cap` #660, 
rearranges relative length units, fixes several minor mistakes and 
adds some line breaks to better manage possible future unit additions.

See https://github.com/w3c/csswg-drafts/pull/902