Feature/smarter where

You can pass arguments to _set_where in a couple of more ways. For example this will work even though you use key => value and string arguments:

    $this->some_model->get_many_by(array(
      'field' => 'value',
      'field' => aray('value', 'another value'), // this will use where_in()
      'field != value',
    ));

You should be able to combine any kind of filter in there.