Replace code directive by the sphinx code-block

[parulin]

The code:: directive is a directive compatible with docutils, allowing less options than the code-block:: or sourcecode:: Sphinx directives.

See this comment: sphinx-doc/sphinx#14411 (comment)

This PR replaces code:: by code-block:: everywhere. Another option is to change only the documentation style guide and the how-to, I'm fine with both.

[unman]

I am somewhat opposed to global changes like this. The results are difficult to review.
In this case I'd like to FIRST discuss the potential benefits to users and THEN move to implement if agreed.
What are the concrete advantages to users of this global change?

[parulin]

I was lazy, tried to batch replace everything to see if it worked and getting no warning, I made this PR. Now, I'm reconsidering it and the few advantages I can find are limited.

I still think it would be good to favor code-block in the rst how-to and style guide, because some options don't work with code (i.e.: the examples of :linenos: and :emphasize-lines: are not functional). To me the main advantage is the emphasize-lines option. There are other options but I'm not sure they are helpful. There is no need to replace the code directive by the code-block one in the other parts of the documentation.

We can also remove the mention to emphasize-lines and correct the linenos example to work with code directive.

What do you think?

[unman]

I thought that the code options were being brought in line with the codeblock options. Sure there is a PR for this.

[parulin]

There are currently two different PRs on the Sphinx side: one keeping things as they are but changing the docs, the other one making code a real alias for code-block. So making such a global change in qubes-doc is obviously wrong right now.

I don't think we can expect them to be shipped in a new Sphinx version very soon, so I would like to just fix the 2 examples where the code directive is wrong in the meantime. That would be a very small PR. Is that okay?