Use form elements in checkbox and radio button groups

* Uses .btn on label elements with nested checkbox and radio controls within
* Updated examples to reflect change in HTML and CSS
* Had to add .active all buttons for proper state highlighting (mimicing the :active pseudo state)
* Still needs JavaScript plugin updated by @fat

less/button-groups.less

@@ -156,3 +156,10 @@
     width: 1%;
   }
 }
+
+
+// Checkbox and radio options
+.btn-group[data-toggle="buttons-radio"] > .btn > input[type="radio"],
+.btn-group[data-toggle="buttons-checkbox"] > .btn > input[type="checkbox"] {
+  display: none;
+}