Automatic hiding/showing without configuration

[noctuid]

Currently automatic-hiding/showing requires manual configuration everywhere (e.g. in the rifle.conf). Generic automatic hiding would require xdotool's blur to work correctly (see #18). Automatic showing would require some sane way to determine the window that gets focus when the dropdown is unfocused and to be notified when that window is closed. I'm guessing this functionality won't be added to xdotool and may be difficult or impossible to implement in a generic way, but it may be worth looking into.

If blur is ever fixed, add a disclaimer that it can be used for automatic-hiding instead of tdrop's mechanism to the readme.