Use towncrier to generate the changelog

[abompard]

Towncrier lets us generate release notes in a much more convenient way than what we currently do. Each PR just has to create a file with the line that should end up in the release notes, and the changelog.rst file can be automatically generated before each release.

I have added documentation in the contributing.rst file for more usage info.

@jeremycline I would also like you to verify that the releasing process I have documented in contributing.rst is correct, please.

[jeremycline]

I made two small commits on top of this to add the package to the dev requirements and to set the docs version automatically. Let me know what you think and revert whatever you don't like :)

If the get-authors.py script needs to be called before the release (it seems like it's supposed to be?) then we should add a note to the release process, too.

This looks super slick! ✨ 🍰

[jeremycline]

I have some fanciness to pull the version in the docs from init.py, I'll push a commit to this PR

[abompard]

That that looks cool. So this line isn't necessary anymore.

[jeremycline]

Do we need to run this before towncrier to generate the authors for a release? If so it'd be good to note that in the release documentation. It'd be cool to auto-generate the contributors to issues and PRs by looking at the news items and querying the PRs/issues for users as well, since bug reports are valuable contributions.

[abompard]

My original intention was that new .author files would be added as part of the PR (just like the news file). But I left this script in case we forgot people and wanted to check before the release. It shouldn't be a requirement, and it needs to be improved before we can use it that way, since at the moment it checks the whole git history, and not since the last tag.

I agree it'd be cool to get contributors from the GitHub API too, I'll see if I can add it in the future.

[jeremycline]

Cool, sounds good to me 😄

[codecov-io]

Codecov Report

Merging #67 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #67   +/-   ##
=======================================
  Coverage   93.08%   93.08%           
=======================================
  Files          11       11           
  Lines         810      810           
  Branches      113      113           
=======================================
  Hits          754      754           
  Misses         37       37           
  Partials       19       19

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[jeremycline]

✨ 🍰