XDG Base Specification

Hello,


I would like to know whether you plan to implement the XDG Base 
Specification for the settings in libgphoto2.

There is already an open ticket [1] for an explanation on some users 
might choose to do so, with further information for example at [2].

I went ahead and created a patch to do that.

Currently the current `$HOME/.gphoto/`  takes precedence (only if 
present) over the $XDG_CONFIG_HOME (and its fallback) as some software 
might not use  `gp_setting_get` to access the settings file.

If this is of no concern then the fallback order can be changed to:

     (1) XDG_BASE_CONFIG/gphoto/settings

     (2) $HOME/.config/gphoto/settings

     (3) $HOME/.gphoto/settings

This should allow for a graceful depreciation of the old settings 
location if this is wanted.

As this only concerns Linux and UNIX systems the Windows portion is 
still unaffected.


[1] https://sourceforge.net/p/gphoto/feature-requests/447/

[2] https://wiki.archlinux.org/title/XDG_Base_Directory


regards,

     lmn