http://www.elasticsearch.org/guide/reference/query-dsl/query-string-query.html
        A query that uses a query parser in order to parse its content.

        > query = ElasticQuery().query_string('this AND that OR thus', default_field='content')

def query_string(cls,
                     query,
                     default_field=None,
                     default_operator=None,
                     analyzer=None,
                     allow_leading_wildcard=None,
                     lowercase_expanded_terms=None,
                     enable_position_increments=None,
                     fuzzy_prefix_length=None,
                     fuzzy_min_sim=None,
                     phrase_slop=None,
                     boost=None,
                     analyze_wildcard=None,
                     auto_generate_phrase_queries=None,
                     minimum_should_match=None):
        '''
        http://www.elasticsearch.org/guide/reference/query-dsl/query-string-query.html
        A query that uses a query parser in order to parse its content.

        > query = ElasticQuery().query_string('this AND that OR thus', default_field='content')
        '''
        instance = cls(query_string={'query': query})
        if default_field is not None:
            instance['query_string']['default_field'] = default_field
        if default_operator is not None:
            instance['query_string']['default_operator'] = default_operator
        if analyzer is not None:
            instance['query_string']['analyzer'] = analyzer
        if allow_leading_wildcard is not None:
            instance['query_string']['allow_leading_wildcard'] = allow_leading_wildcard
        if lowercase_expanded_terms is not None:
            instance['query_string']['lowercase_expanded_terms'] = lowercase_expanded_terms
        if enable_position_increments is not None:
            instance['query_string']['enable_position_increments'] = enable_position_increments
        if fuzzy_prefix_length is not None:
            instance['query_string']['fuzzy_prefix_length'] = fuzzy_prefix_length
        if fuzzy_min_sim is not None:
            instance['query_string']['fuzzy_min_sim'] = fuzzy_min_sim
        if phrase_slop is not None:
            instance['query_string']['phrase_slop'] = phrase_slop
        if boost is not None:
            instance['query_string']['boost'] = boost
        if analyze_wildcard is not None:
            instance['query_string']['analyze_wildcard'] = analyze_wildcard
        if auto_generate_phrase_queries is not None:
            instance['query_string']['auto_generate_phrase_queries'] = auto_generate_phrase_queries
        if minimum_should_match is not None:
            instance['query_string']['minimum_should_match'] = minimum_should_match
        return instance