Introduce file-based user configuration

[jotaen]

This PR addresses #158.

klog now looks for a config file at ~/.klog/config.yml, where users are able to specify some preferences. For now, that is:

• default_rounding: the value for the --round flag, unless specified, e.g. in klog start or klog stop.
• default_should_total: the default for the --should-total flag, unless specified, that is used whenever klog creates a new record, e.g. in klog create, but also in klog track or klog start, as these might create new records on the fly.

More configuration parameters may follow later, now that the groundwork is set up.

When the config file is absent, everything behaves as before, so it’s strictly optional right now.

What’s also new is that klog will respect the $KLOG_FOLDER_LOCATION or $XDG_CONFIG_HOME environment variables, if set. In this case, and when users have bookmarks, then this will be a breaking change. The fix is for them to manually move over their bookmarks.json file to the new klog folder location. I’ll take note in the Changelog about this.

The klog config command is hidden from the help output for now, but it can be invoked nevertheless on the nightly build (when compiling klog from the main branch). I’ll do some more testing, refactoring, and enhancements in the next time, and plan to include this with the next release – probably within the next few weeks.

[ulken]

Awzum sauce! Nice choice of starter settings as well 😁

One minor nitpick: The name of the env var sticks a little. The suffix _FOLDER_LOCATION feels unfamiliar/unconventional. Any particular reason not to go with more established _HOME (JAVA_HOME, XDG_CONFIG_HOME) or PATH (MANPATH, GOPATH)?

[jotaen]

Good question. I realized that it’s probably a good idea to look into this whole config folder topic more properly anyway before the next release, so → #250.