Adopt newsfragments pattern currently used in trio codebase (and maybe use towncrier)

[pipermerriam]

What is wrong?

For each PR we have to also push a commit to the release notes. I'm not loving the workflow. I find it easy to forget to do.

How can it be fixed

Take a look at this: https://github.com/python-trio/trio/tree/master/newsfragments

I believe it uses this tools to aggregate it: https://pypi.org/project/towncrier/

I think this would be a more reliable way to aggregate these changes and it is friendly to 3rd party contributors.

[pipermerriam]

cc @lithp @carver @cburgdorf @ralexstokes

[carver]

Related: #101

[carver]

I think this looks the most like the gitlab-writeup that veox ponted to:

For this reason, GitLab generates their change log from contributor-provided snippets. The reasoning section is at the very end, but highlights a few rakes, so not worth skipping.

So probably worth a re-read of that post before changing the process.

[carver]

I just did a re-read of the reasoning, and of our conversation in 101. I think maybe some resistance was about the data being structured, which it appears the towncrier approach doesn't require (except for rst format, which isn't really a new constraint, and the filename format).

So I'm 👍 to switch if others are. It looks quite similar in output to our current release note approach, anyway.

[cburgdorf]

I support this and I happily volunteer to set it up if we agree we want it.

[pipermerriam]