(www-format-value): Add the first variable `object' and the second

(www-format-value): Add the first variable `object' and the second
variable `feature-name'; change variable `variable' to optional;
modify for `www-format-apply-value'.
(www-format-apply-value): Add the first variable `object' and the
second variable `feature-name'; support format `wiki-text'.
(www-format-eval-feature-value): Modify for `www-format-apply-value'.
(www-format-eval-unit): Likewise.
(www-xml-format-props): New function.
(www-xml-format-unit): New function.
(www-xml-format-list): New function.