Platformdirs

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- site_cache_dir use ``/var/tmp`` instead of ``/var/cache`` on unix, as the later may be write protected

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- Introduce ``site_cache_dir``

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- Add ``appdirs`` keyword to package

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- **BREAKING** Changed the config directory on macOS to point to ``*/Library/Application Support``
- macOS: remove erroneous trailing slash from ``user_config_dir`` and ``user_data_dir``

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- Fix missing ``typing-extensions`` dependency.

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- Add detection of ``$PREFIX`` for android.