Update HTML docs

[mjambon]

I forgot to run make doc with the last PR after changing the Testo module interface slightly.

PR checklist:

• [x] Purpose of the code is evident to future readers
• [x] Tests are included or a PR comment includes a reproducible test plan
• [x] Documentation is up-to-date
• [x] A changelog entry was added to CHANGES.md for any user-facing change

Check out CONTRIBUTING.md for more details.

[aryx]

Can we see the doc somewhere? (I mean the rendered html).

[mjambon]

yes. 😀

[mjambon]

There's a link in the project's readme.