Usage
 * 
 * 
 * new OptionsetField(
 *    $name = "Foobar",
 *    $title = "FooBar's optionset",
 *    $source = array(
 *       "1" => "Option 1",
 *       "2" => "Option 2",
 *       "3" => "Option 3",
 *       "4" => "Option 4",
 *       "5" => "Option 5"
 *    ),
 *    $value = "1"
 * );
 * 
 * 
 * You can use the helper functions on data object set to create the source array. eg: 
 * 
 * 
 * //Database request for the object
 * $map = FooBar::get()->map();
 *  // returns an SS_Map object containing an array of ID => Title
 *
 * // Instantiate the OptionsetField 
 * $FieldList = new FieldList(
 *   new OptionsetField(
 *    $name = "Foobar",
 *    $title = "FooBar's optionset",
 *    $source = $map,
 *    $value = $map[0]
 *   )
 * );
 *
 * // Pass the fields to the form constructor. etc
 * 
 * 
 * @see CheckboxSetField for multiple selections through checkboxes instead.
 * @see DropdownField for a simple