Handle single widget arguments to force (#29)

* Handle single widget arguments to force
* update README (force/single-use)

README.md

@@ -125,10 +125,12 @@ enable caching of values returned by a widget type
 **Force update of widgets:**
 
 ```Lua
-    vicious.force({ widget, })
+    vicious.force(widget)
+    vicious.force({ widget1, widget2 })
 ```
 
-widget argument is a table with one or more widgets that will be updated
+widget argument is a single widget or a table with one or more widgets that
+will be updated
 
 
 Widget types

init.lua

@@ -234,6 +234,8 @@ function vicious.force(wtable)
         for _, w in pairs(wtable) do
             update(w, nil, true)
         end
+    else
+       update(wtable, nil, true)
     end
 end
 -- }}}