Change location of klog config folder

[jotaen]

Resolves #250.

The lookup order for klog’s config folder (previously referred to as “klog folder”, residing at ~/.klog by default on all OS’es) is now this:

• macOS:
  • $KLOG_CONFIG_HOME (expects full path including the “suffix” bit, so you can also set it to be /foo/bar/all-my-klog-configs if that fancies you)
  • $XDG_CONFIG_HOME/klog (for XDG-addicts that stranded on macOS for some reason)
  • $HOME/.klog (the default / most “idiomatic” config location on macOS for CLI apps)
• Linux:
  • $KLOG_CONFIG_HOME (see above)
  • $XDG_CONFIG_HOME/klog
  • $HOME/.config/klog (the default / most “idiomatic” config location on Linux)
• Windows
  • %KLOG_CONFIG_HOME% (see above)
  • %AppData%\klog (the default / most “idiomatic” config location on Windows)

klog iterates through these respective locations, and the first env var that’s set wins. klog will look for (and potentially initialise) the config folder at that location.

By doing klog --config-folder, you can see which one it chose, and it also prints the lookup order for reference – e.g., on macOS:

$ klog --config-folder
/Users/jan/.klog
(Lookup order: $KLOG_CONFIG_HOME, $XDG_CONFIG_HOME/klog, $HOME/.klog)

For the env var name, I eventually settled on KLOG_CONFIG_HOME, as I find that most clear and straightforward.