User-level settings

[seeM]

via @jph00

how about for the location we follow the XDG spec?

$XDG_CONFIG_HOME defines the base directory relative to which user-specific configuration files should be stored. If $XDG_CONFIG_HOME is either not set or empty, a default equal to $HOME/.config should be used.

I've just added a new module fastcore.xdg to make this more convenient.