Use pathlib for file args to support Windows and Linux.

[ntouran]

This uses pathlib instead of os.path and enables paths to be either Windows or Linux style.

Fixes #57.

[ntouran]

Only the linter god needs to give his/her okay.

Trying to see the issue here. Looks like the linter failed to install its own environment before being able to actually lint?

               raise RuntimeError("The Poetry configuration is invalid:\n" + message)
          RuntimeError: The Poetry configuration is invalid:
            - [extras.pipfile_deprecated_finder.2] 'pip-shims<=0.3.4' does not match '^[a-zA-Z-_.0-9]+$'

          [end of output]

      note: This error originates from a subprocess, and is likely not a problem with pip.
    error: metadata-generation-failed

    × Encountered error while generating package metadata.
    ╰─> See above for output.

Not sure there's anything I can do about that on my end?