Implement a command that can work with multiple files

[simonw]

https://github.com/Jonty/uk_petitions_data/tree/master/petitions/2019-_Conservative_government is a great example of a Git scraper that maintains a separate file for each scraped object.

This is why I renamed the initial command to git-history file ... in #4 - it leaves space for other commands that can do other operations.

[simonw]

This could be a good example too: https://github.com/glassechidna/trackiam/tree/master/services

It's not a file per tracked item, but it does show data spread across many different files.