Print current directory to stdout when quitting GUI and UI

[aduros]

With this it would be possible to use duc as a directory explorer and plug into all kinds of external tools.

One simple example (zshrc or bashrc):

cduc () {
    cd "`duc gui`"
}

It would also make it possible to build integrations with other file explorers like lf and ranger.

Relates to #247

[zevv]

For duc gui that should be possible, but since the ui itself is rendered using stdout, this will not fly for duc ui

[aduros]

Ah yeah, makes sense.