git: add support for a single commit/reference #3
Description
Many git reference types just work with the existing ucd -a/-b arguments, including things like -a $COMMIT_HASH and -b 'main~3' (three commits before the tip of the main branch).
However, git's diff mechanism when comparing two references is exclusive to the first reference and inclusive of the second commit. This can cause a problem when wanting to include the initial commit as there's not (that I could see) a way to reference immediately prior to the initial commit, neither ~ nor ^ are accepted by git on the initial commit. Being able to do something like ucd --commit HASH git . (or --reference?) might be a nice shortcut and solve this specific initial commit problem.