Add more examples to HTML test page

[thibaudcolas]

Is your proposal related to a problem?

The HTML test page doesn’t contain unusual / unsupported formats – it needs to have more test content. Ideally everything covered by https://github.com/bryanbraun/poor-mans-styleguide.

Describe the solution you’d like

Copy-paste relevant example content from https://github.com/bryanbraun/poor-mans-styleguide.