Feature request: Publish commit comments

[RandomFractals]

see extensive followup on this from @mbostock here:

lost notebook

We’re planning a history feature to show how a notebook has changed over time. Authors will be able to browse every version, while readers will only be able to see published versions. Authors will also be able to restore work, say by reverting to an earlier version or cherry-picking changes. And forking, too, of course. For this to work well, I expect we’ll want a way of attaching notes to specific versions (the equivalent of git tags or commit messages), since the number of automatically-saved…