api_to_html.php. Third party libraries need to be updated

[dac514]

In PHP 7.1 I get:

PHP Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; Markdown_Parser has a deprecated constructor in C:\Users\dac\Code\github\renoise\xrnx\Xtra\HtmlGen\includes\markdown\markdown.php on line 215

PHP Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; MarkdownExtra_Parser has a deprecated constructor in C:\Users\dac\Code\github\renoise\xrnx\Xtra\HtmlGen\includes\markdown\markdown.php on line 1677

PHP Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; GeSHi has a deprecated constructor in C:\Users\dac\Code\github\renoise\xrnx\Xtra\HtmlGen\includes\geshi\geshi.php on line 259

The script still works but probably not for long.