Add possibility to search in specific field(s)

Example:
$pages = \Nos\Page\Model_Page::find('all', array(
    'where' => array(
        'keywords_fields' => array(
            'page_title'        => 'keyword1 keyword2',
            'wysiwygs->content' => 'keyword3',
            '*'                 => 'keyword4',
        ),
    ),
));
Bugfix
default title boost
Merge branch 'feature/search_in_specific_field'
Merge remote-tracking branch 'github_rw/master'
Documentation for version 1.2