[TASK] Use valid HTML comment delimiters

This changes the comment end delimiter to '---->' (without '!') to avoid
parsing errors due to HTML comment cleanup as done by some extensions
like EXT:sourceopt and to meet the HTML comment syntax as described by
the W3C: http://www.w3.org/TR/html-markup/syntax.html#comments
Merge pull request #203 from tbal/htmlcomments

[TASK] Use valid HTML comment delimiters