add check and radio controls

luigi/widget/check.lua

@@ -0,0 +1,18 @@
+--[[--
+A check box.
+
+@widget check
+--]]--
+
+return function (self)
+    self:onPress(function ()
+        self.value = not self.value
+    end)
+
+    self:onChange(function ()
+        local subtype = self.value and 'check.checked' or 'check.unchecked'
+        self.type = { 'check', subtype }
+    end)
+
+    self.value = not not self.value
+end