Add CHANGELOG.md and use towncrier for automatic assembly

[tjanez]

Closes #759.

[codecov]

Codecov Report

Merging #2496 into master will increase coverage by 0.15%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2496      +/-   ##
==========================================
+ Coverage   67.06%   67.21%   +0.15%     
==========================================
  Files         324      324              
  Lines       29880    29880              
==========================================
+ Hits        20038    20085      +47     
+ Misses       7360     7322      -38     
+ Partials     2482     2473       -9

Impacted Files	Coverage Δ
go/consensus/tendermint/roothash/roothash.go	63.67% <0%> (-6%)	⬇️
go/worker/txnscheduler/committee/node.go	70.3% <0%> (-2.63%)	⬇️
go/storage/metrics.go	74.13% <0%> (-2.59%)	⬇️
go/storage/client/client.go	71.37% <0%> (-1.09%)	⬇️
go/worker/merge/committee/node.go	74.63% <0%> (-0.25%)	⬇️
go/consensus/tendermint/tendermint.go	64.22% <0%> (+0.71%)	⬆️
go/worker/registration/worker.go	65.51% <0%> (+0.94%)	⬆️
go/runtime/transaction/transaction.go	78.04% <0%> (+1.21%)	⬆️
go/worker/common/committee/group.go	82.52% <0%> (+1.48%)	⬆️
go/worker/common/p2p/p2p.go	71.17% <0%> (+2.7%)	⬆️
... and 7 more

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[kostko]

Cool!

The lint on GitHub Actions seems to be failing though, seems like some issue with the remote branch not being fully fetched? Probably an explicit git fetch origin <BASE-BRANCH> is needed because the linter tries to inspect what changed from the base branch.

[kostko]

What about when you want to do an actual release?

[tjanez]

You would leave out the --draft argument and towncrier would stage the changes, i.e. remove the Change Log fragments and add a new section to the CHANGELOG.md.
After verifying that everything looks ok, you would just commit the changes.

I plan to create changelog Make target that would call towncrier underneath to make things even simpler.

[pro-wh]

can we have this not say 19.0 (2019-12-18) is the initial release? it's not the initial release. if we don't want to go back and retroactively describe what changed between a9a532e and 19.0, it's less confusing not to have this section at all

[tjanez]

Agreed, this is not ideal. I would still like to have this section so that readers will know what the Change Log section for the next release, i.e. 19.1, refers to.

I've changed the contents to actually describe a process change, i.e. that the project started using a new versioning and release process and adopted a CalVer (calendar versioning) scheme. The latter also explains why this release has version 19.0 as opposed to 1.0 or similar.

Please, take another look.

[pro-wh]

thx for the changes

[tjanez]

The lint on GitHub Actions seems to be failing though, seems like some issue with the remote branch not being fully fetched? Probably an explicit git fetch origin <BASE-BRANCH> is needed because the linter tries to inspect what changed from the base branch.

Yes, indeed the GitHub Checkout action only fetches the pull request branch by default. Added a command that manually fetches the master branch.

Warren ACKed the PR via Slack