add "gravity" option for bar

A bar must be full-screen-width (or height, for vertical bars) to
have an "exclusive zone", otherwise it appears on top of other windows
instead of moving them out of the way. To right-justify (or bottom-
justify) the indicators in a bar, add :gravity :end to its options

Am *probably* going to get rid of this again, in favour of adding
support for "spacers" in the bar - then the same bar could contain
both left- and right-justified indicators

blinkenlicht/bl.fnl

@@ -23,8 +23,12 @@
 
 (bar
  {
-  :anchor [:top :right]
+  ;; bar must be full width to set up an "exclusive zone" (moves
+  ;; other windows out of the way), otherwise it will display on
+  ;; to of whatever's on the screen already
+  :anchor [:top :right :left]
   :orientation :horizontal
+  :gravity :end
   :classes ["hey"]
   :indicators
   [

blinkenlicht/blinkenlicht.fnl

@@ -135,7 +135,9 @@
 
 (local bars [])
 
-(fn bar [{ : anchor : orientation : indicators :  classes }]
+(fn bar [{: anchor : orientation : indicators
+          : gravity
+          : classes }]
   (let [window (Gtk.Window  {} )
         orientation (match orientation
                       :vertical Gtk.Orientation.VERTICAL
@@ -145,6 +147,9 @@
       (add-css-classes ["bar"])
       (add-css-classes (or classes [])))
 
+    (if (= gravity :end)
+        (box:pack_start (Gtk.EventBox) true true 0))
+
     (table.insert bars { : window : anchor : indicators })
     (each [_ i (ipairs indicators)]
       (box:pack_start i.button false false 0))