* Add a new HTML_VERSION parameter to HTMLCleanerConfiguration.
* Pass the HTML version in DefaultHTMLCleaner to HTMLCleaner and set the document type accordingly.
* Add a tag transformation to transform `<tt>` to `<span class="monospace">`.
* Add a tag transformation to replace the font filter in HTML5 as the cleaner removes the font tags too early otherwise.
* Extend BodyFilter to allow more HTML5 tags directly in the body.
* Add constants for many HTML5 tags in HTMLConstants.
* Add a new unit test HTML5HTMLCleanerTest to test the behavior of HTMLCleaner with the HTML5 configuration.
* Modify DefaultHTMLCleanerTest to allow re-using most test methods in HTML5HTMLCleanerTest.