Updating pandoc flags

[kjvbrt]

Updating pandoc flags to use --markdown-headings=atx instead of deprecated --atx-headers.

[mwouts]

Hi @kjvbrt , thank you for this contribution. In which version of pandoc was this change introduced? I am afraid we'll have to require that version of pandoc in both our test suite and also on site for users.

[kjvbrt]

Ahh sorry, the version of pandoc which introduced this change is 2.11.2 (2020-11-19).

[mwouts]

Thanks @kjvbrt for that information, that is very helpful. What is the impact for you of using the deprecated form? Does this cause a warning when you use jupytext? Of course I think it is a good idea to use the new option --markdown-headings, but I am not sure how many users have recent versions of Pandoc...

[kjvbrt]

Yeah, it comes down to the platform you want to support. We are running jupytext on centos7, which has ancient pandoc 1.12.3.1 and have to install more modern version anyway since jupytext requires versions from 2.7.2. On ubuntu 22.04LTS the pandoc version is 2.9.2.1 and on CentOS 8 it is 2.0.6. Considering support for those two platforms the PR is probably better for later.