Allow Minion_Task::factory($string) with Minion_Task::factory($array)

Now Minion_Task must be called as

    Minion_Task::factory(array('task'=>'task:name'))->
        execute(array('option1'=>"foo", 'option2'=>"bar"));

I suggest using a simplified form with this

    Minion_Task::factory('task:name')->
        execute(array('option1'=>"foo", 'option2'=>"bar"));