Show-in-file-manager

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- Drop setup.py and setup.cfg in favor of pyproject.toml.
- Purge doc directory.
- New build dependency: [argparse-manpage](https://github.com/praiskup/argparse-manpage)
- Generate man page with argparse-manpage instead of pandoc.
- Format and lint using ruff. Drop black.
- Drop Python 3.6 and 3.7 support.

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- Move debian directory into doc

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- Fix bug [3](https://github.com/damonlynch/showinfilemanager/issues/3):
Missing dependency on packaging.

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- Add check for "unity:unity7:ubuntu" in environment variable
XDG_CURRENT_DESKTOP.
See https://github.com/damonlynch/rapid-photo-downloader/issues/46.

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- Add `allow_conversion` switch to `show_in_file_manager()`. Set to False
if passing non-standard URIs.
- Recognize non-standard URI prefix 'camera:/', used by KDE.
- Added function `linux_desktop_humanize()`, to make Linux desktop environment
variable name values human friendly.

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- On WSL2, use a Linux file manager (if set) for WSL paths, and Windows
Explorer for Windows paths. If no Linux file manager is installed, use
Windows Explorer. To override the default choice of using Explorer for
Windows paths, simply specify a file manager of your choice.
- On both WSL1 and WSL2, use Windows style URIs to work around a
[bug](https://github.com/microsoft/WSL/issues/7603) in WSL where using
the /select switch while passing a path with spaces in it fails.
- Don't mess up the terminal when launching Windows Explorer from WSL
on Windows Terminal.