Add newfeh (feh wrapper) to PrintScreen button

Because changing desktop background via shortcut is badass.  (And using
PrintScreen for that is even clever.)

dotfiles/i3/config

 bindsym $mod+m              exec "$spn bmo menu status"
 bindsym $mod+Shift+m        exec "i3-dmenu-desktop --dmenu='bmo dmenu'"
 bindsym $mod+o              exec "$spn bmo menu context"
+bindsym $mod+Print          exec "newfeh"
 
 
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