(www-parse-string-as-space-separated-ids): New function.
(www-parse-string-as-ku-ten): New function.
(www-feature-parse-string): Support `space-separated-ids' and
`ku-ten'.

update.

(www-feature-value-format): Return 'space-separated-ids for
`structure' type features.
(www-format-value-as-ids): New function.
(www-format-apply-value): Use `www-format-value-as-ids' for format
`space-separated-ids'.

New file.

New files.