Auditorium

* Added command `auditorium render` to generate a static HTML that can be displayed without `auditorium`.

* Fixed random order of vertical slides.

* Changed the syntax for vertical slides, thanks to suggestions by [tialpoy](https://www.reddit.com/user/tialpoy/).
* Added automatically launching browser on `auditorium run` and `... demo`. Override with `--launch=0`.
* Improved performance, now rendering only occurs at `show.run` or when changing the theme.

* Improved test coverage a lot.

* Added support for interpolating Python variables in Markdown mode.

* Ported to Sanic 🤓!