This cleans up the home directories of users and helps making sure that
Coursier's cache is not accidentically backed up by applications or OS
functionality.
The precedence is as follows:
- existing $COURSIER_CACHE environment variable
- existing coursier.cache Java property
- existing operating system specific standards:
- Linux: $XDG_CACHE_HOME/coursier, with fallback to ~/.cache/coursier
- Windows: {SpecialFolder.LocalApplicationData}/cache/Coursier
- macOS: $HOME/Library/Caches/Coursier
- existing ~/.coursier/
- fallback to operating system specific standard directory else.
See discussion in https://github.com/coursier/coursier/pull/676#issuecomment-338974822