Add 2 x middle-mouse-button actions

1) Middle-mouse-click on client in the tasklist to close it

2) Middle-mouse-click on client titlebar to close it

rc.lua.template

@@ -158,6 +158,7 @@ awful.util.tasklist_buttons = my_table.join(
             c:raise()
         end
     end),
+    awful.button({ }, 2, function (c) c:kill() end),
     awful.button({ }, 3, function ()
         local instance = nil
 
@@ -690,6 +691,7 @@ client.connect_signal("request::titlebars", function(c)
             c:emit_signal("request::activate", "titlebar", {raise = true})
             awful.mouse.client.move(c)
         end),
+        awful.button({ }, 2, function() c:kill() end),
         awful.button({ }, 3, function()
             c:emit_signal("request::activate", "titlebar", {raise = true})
             awful.mouse.client.resize(c)