Feature request: optionally keep optional closing tags and self-closing tags

[YodaDaCoda]

Tags
Optional opening and closing tags are removed.

Tangential to #192

This project is awesome but I'm unable to use it for minifying xhtml because it strips optional closing tags and removes the trailing / from self-closing tags. So much of the behaviour is already able to be customised, it seems an oversight that this cannot be. I'd love it if those functions could optionally be disabled.