Per-Commit stepping and baseline improvement

[Byron]

Various tasks offloaded from #26 with the main purpose of restoring the correct order of crate changes and updating the baseline tests to be more realistic.

Tasks

1. add support for per-commit stepping to allow for orderly discovery of changes
2. improve baseline to test big steps and one-commit-per-step (using the new API of above) like ---x---x---xxx
3. adjust baseline test to inform about the yanked status as well, so we expect that all changes leave us as exactly the right information about the versions still in existence and their yanked status.