lib.awful.widget: Return obj in set_* methods

This change enables stuff like the following:

 awful.widget.graph({}):set_color("red"):set_width(40):add_value(0.5)

Additionally, one can use the above directly in th widgets table.

This most likely doesn't break any existing configs and it adds a quite nice
syntax which can be used for in-place configuration of new widgets.

Signed-off-by: Uli Schlachter <psychon@znc.in>
Signed-off-by: Julien Danjou <julien@danjou.info>

lib/awful/widget/graph.lua.in

@@ -164,6 +164,7 @@ local function add_value(graph, value)
     end
 
     update(graph)
+    return graph
 end
 
 
@@ -175,6 +176,7 @@ local function set_height(graph, height)
         data[graph].height = height
         update(graph)
     end
+    return graph
 end
 
 --- Set the graph width.
@@ -185,6 +187,7 @@ local function set_width(graph, width)
         data[graph].width = width
         update(graph)
     end
+    return graph
 end
 
 -- Build properties function
@@ -193,6 +196,7 @@ for _, prop in ipairs(properties) do
         _M["set_" .. prop] = function(graph, value)
             data[graph][prop] = value
             update(graph)
+            return graph
         end
     end
 end

lib/awful/widget/progressbar.lua.in

@@ -116,6 +116,7 @@ end
 local function set_value(pbar, value)
     local value = value or 0
     data[pbar].value = math.min(1, math.max(0, value))
+    return pbar
 end
 
 --- Set the progressbar height.
@@ -126,6 +127,7 @@ local function set_height(progressbar, height)
         data[progressbar].height = height
         update(progressbar)
     end
+    return progressbar
 end
 
 --- Set the progressbar width.
@@ -136,6 +138,7 @@ local function set_width(progressbar, width)
         data[progressbar].width = width
         update(progressbar)
     end
+    return progressbar
 end
 
 -- Build properties function
@@ -144,6 +147,7 @@ for _, prop in ipairs(properties) do
         _M["set_" .. prop] = function(pbar, value)
             data[pbar][prop] = value
             update(pbar)
+            return pbar
         end
     end
 end