Have `scriv create` pull from known sources of words

[cpennington]

scriv create could pull from git commit messages (easy-ish) and Github PR descriptions (harder) to pre-populate the changelog fragment. If those commits/PRs are tagged correctly, scriv could add the existing words to the pre-populated sections of the fragment.

[nedbat]

https://www.conventionalcommits.org/en/v1.0.0/ is a popular spec for how to structure commit messages.

[nedbat]

This command finds the full commit messages from all of the recent commits since the last one that added a fragment:

git log --format='%B' $(git log -1 --format=%H --diff-filter=A -- changelog.d)..

[medecau]

Hey @nedbat I took that command you shared and put it in a script. Then went a bit too far and made the whole thing generate CHANGELOG files.

Anyway here is the gist for that: https://gist.github.com/medecau/da827533390abcc32c91f11c4d5bb34d

Maybe some of that can be brought into scriv?