and made some other minor changes.

- Introduced data-url shortcode
- Fixed test data links
- Markdownify text in shortcodes (e.g. image captions, data-url)

- Theory for analytical solution.
- Comparison-images to analytical solution.

Correct the reference to the image in elder benchmark description.

Uniqueness of titles are required in the same menu section (benchmarks)

Use png for images. Fix sections in the markdown.