(sgml-namify-char): New cmd.

(sgml-namify-char): New cmd.
(sgml-name-char): Use it.
(sgml-tag-last, sgml-tag-history): New vars.
(sgml-tag): Use them.
(sgml-skip-tag-forward): Use sgml-tag-syntax-table.
(sgml-delete-tag): Remove resulting empty lines.
(sgml-tag): Don't make intangible.
(sgml-parse-tag-backward): Add limit argument.
(html-autoview-mode): Use define-minor-mode.