Improvement: Make the CLI work on windows

[cyclotruc]

I did't have windows in mind when I started this; and I have little to no experience on that matter, so any help on this matter would be greatly appreciated.

I think Windows user for the Pypi package (CLI or python module) will be more and more common, since it's often the platform of beginners who use gitingest to learn about codebases

From the few tests I did it seems that \ and things such as C: in paths are not handled
This should be easily solvable by using the proper os API or maybe pathlib

[gustaveWPM]

Hummm...
It's a common and frustrating issue.

I think a good way to fix it would also be to write unit tests that cover all the CLI features that handle paths and other OS-specific details.

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It would then be possible to test them across multiple operating systems (Windows, macOS, Linux) using a Matrix in a GitHub Action.
https://docs.github.com/en/actions/writing-workflows/choosing-what-your-workflow-does/running-variations-of-jobs-in-a-workflow

As it has been done to check several Python versions here: https://github.com/cyclotruc/gitingest/blob/main/.github/workflows/unitest.yml#L14