(xml-lite-at-indentation-p): Move.

(xml-lite-at-indentation-p): Move.
(xml-lite-in-string-p, xml-lite-looking-back-at, xml-lite-looking-at):
New functions.
(forward-xml-tag, backward-xml-tag, beginning-of-xml-tag)
(end-of-xml-tag): Remove.
(xml-lite-get-context): Better handling of comments.
(xml-lite-calculate-indent): Use xml-lite-in-string-p.
(xml-lite-parse-tag-backward): Rewrite.