Only show Super+B notification while B is pressed

Hide the notification as soon as the B key is released.  This is kind of
neat, but we'll have to see if it's actually convenient.  If it turns
out it is, there are some kinks to work out.

Also see <dunst-project/dunst#284>.

home/xbindkeysrc

@@ -148,11 +148,19 @@
 "lock"
    XF86ScreenSaver
 
-# These notifications are excluded from Dunst's history based on the "ephemeral" category.
-# There is associated configuration in `home/config/dunst/dunstrc` that makes this work.
-"notify-send -u low -t 0 -c ephemeral - "$(date -u +$'%A, %B %-d\n<b>%H:%M</b>') UTC · $(TZ=Europe/Berlin date +'<b>%H:%M</b>') Berlin · $(TZ=Asia/Taipei date +'<b>%H:%M</b>') Taipei"$'\n\n'"$(bat)""
+# Show a "date and battery info" desktop notification.  FIXME: This doesn't work correctly
+# until I run `xset -r 56`, which disables autorepeat for the B key globally.  That's an
+# ugly workaround of course.  TODO: take a look at what sxhkd can do.  Also, these
+# notifications are currently no longer excluded from Dunst's history because Dunstify
+# doesn't seem to have an equivalent to the `--category` option of `notify-send`.
+"dunstify -u low -t 0 -r 84873362 - "$(date -u +$'%A, %B %-d\n<b>%H:%M</b>') UTC · $(TZ=Europe/Berlin date +'<b>%H:%M</b>') Berlin · $(TZ=Asia/Taipei date +'<b>%H:%M</b>') Taipei"$'\n\n'"$(bat)""
    Mod4 + b
 
+# We only show this "date and battery info" notification while the B key is held down and
+# close it as soon as the key is released.
+"dunstify --close 84873362"
+   Mod4 + b + Release
+
 "vimsel"
    Mod4 + e
 
@@ -168,6 +176,8 @@
 "xterm -name 'floating xterm' -geometry 180x29 -e htop"
    Mod4 + apostrophe
 
+# These notifications are excluded from Dunst's history based on the "ephemeral" category.
+# There is associated configuration in `home/config/dunst/dunstrc` that makes this work.
 "notify-send -u low -t 0 -c ephemeral - "$(date -u +$'%A, %B %-d\n<b>%H:%M</b>') UTC · $(TZ=Europe/Berlin date +'<b>%H:%M</b>') Berlin · $(TZ=Asia/Taipei date +'<b>%H:%M</b>') Taipei""
    Mod4 + z