Add Deprecation Roadmap to backward compatibility document

[nicoddemus]

We should replace the wiki document to a link to this document now: https://github.com/pytest-dev/pytest/wiki/Deprecation-Roadmap

Rationale: the Wiki is not really used by us so I doubt users look at it, plus deprecation always involves code so it makes sense to update the document in the same PR.

[coveralls]

Coverage remained the same at 92.258% when pulling f9029f1 on nicoddemus:deprecation-roadmap-docs into 74aaf91 on pytest-dev:master.

[nicoddemus]

@flub @RonnyPfannschmidt @The-Compiler @hackebrot

[hackebrot]

Hi @nicoddemus! 👋

I'm not entirely sure about what order I prefer. If we're going to keep it at just two versions it probably doesn't make too much difference, but if we're going to extend the list, I'd like to see the upcoming release first, then any future releases, followed by a section for deprecations in past versions.

[nicoddemus]

Hi @hackebrot!

I'd like to see the upcoming release first, then any future releases, followed by a section for deprecations in past versions.

This is the order that is in the document already... would you like me to change something? It is not very clear to me from your comment if you want me to change something.

[hackebrot]

I think I'd add section headers

• Upcoming Release
• Future Releases
• Past Releases

Or describe the order in the section description.

[nicoddemus]

@hackebrot added Future/Past releases as you suggested. I didn't add a "upcoming" release because I think it will be tedious to maintain it for each release, seems better to just explicitly declare in which versions some things will be removed.

[hackebrot]

LGTM 👍

[coveralls]

Coverage remained the same at 92.258% when pulling b0f558d on nicoddemus:deprecation-roadmap-docs into 74aaf91 on pytest-dev:master.

[nicoddemus]

Thanks for the review! 👍