Parse config for log_format directives
    :return: iterator over ('format name', 'format string') tuple of found directives

def get_log_formats(config):
    """
    Parse config for log_format directives
    :return: iterator over ('format name', 'format string') tuple of found directives
    """
    # log_format name [params]
    log_format = Literal('log_format') + parameter + Group(OneOrMore(parameter)) + semicolon
    log_format.ignore(pythonStyleComment)

    for directive in log_format.searchString(config).asList():
        name = directive[1]
        format_string = ''.join(directive[2])
        yield name, format_string