API: added force() function to force update widgets

New function introduced vicious.force({ widget, }) - widget argument
is a table with one or more widgets that will be updated.

README

@@ -82,6 +82,12 @@ Enable caching of a widget type:
 
     - enable caching of values returned by a widget type
 
+Force update of widgets:
+  vicious.force({ widget, })
+
+    - widget argument is a table with one or more widgets that will be
+      updated
+
 
 Power and Caching
 -----------------

init.lua

@@ -72,6 +72,7 @@ for i, w in pairs(_M) do
 end
 -- }}}
 
+
 -- {{{ Local functions
 -- {{{ Update a widget
 local function update(widget, reg, disablecache)
@@ -170,6 +171,7 @@ end
 -- }}}
 -- }}}
 
+
 -- {{{ Exposed functions
 -- {{{ Register a widget
 function register(widget, wtype, format, timer, warg)
@@ -245,6 +247,16 @@ function cache(type)
 end
 -- }}}
 
+-- {{{ Force update of widgets
+function force(widgets)
+    if type(widgets) == "table" then
+        for _, w in pairs(widgets) do
+            update(w, nil, true)
+        end
+    end
+end
+-- }}}
+
 -- {{{ Suspend all widgets
 function suspend()
     for w, i in pairs(registered) do