Use a different tool for html-beautifying.

[armcburney]

The gem we're using currently for beautification doesn't support html5 unfortunately. We should do some investigation into tools which support html5 beautification as well (or we could make a PR to the gem to support html5 😉).

[davepagurek]

We could pass in an indentation level to to_html and make tags auto-indent sub tags? would be pretty quick and would mean no outside dependencies are needed

[armcburney]

Yeah, that could work!

[armcburney]

Since we're using C++ now, we can use the html5 variant of Tidy: https://github.com/htacg/tidy-html5