Render given template string and return the result.

        :param template: Template content
        :param context: A dict or dict-like object to instantiate given
            template file
        :param is_file: True if given `template` is a filename
        :param at_paths: Template search paths
        :param at_encoding: Template encoding
        :param kwargs: Keyword arguments passed to jinja2.Envrionment. Please
            note that 'loader' option is not supported because anytemplate does
            not support to load template except for files

        :return: Rendered string

def _render(self, template, context, is_file, at_paths=None,
                at_encoding=ENCODING, **kwargs):
        """
        Render given template string and return the result.

        :param template: Template content
        :param context: A dict or dict-like object to instantiate given
            template file
        :param is_file: True if given `template` is a filename
        :param at_paths: Template search paths
        :param at_encoding: Template encoding
        :param kwargs: Keyword arguments passed to jinja2.Envrionment. Please
            note that 'loader' option is not supported because anytemplate does
            not support to load template except for files

        :return: Rendered string

        """
        eopts = self.filter_options(kwargs, self.engine_valid_options())
        self._env_options.update(eopts)

        # Use custom loader to allow glob include.
        loader = FileSystemExLoader(at_paths, encoding=at_encoding.lower(),
                                    enable_glob=True)
        env = jinja2.Environment(loader=loader, **self._env_options)
        if kwargs:
            context.update(kwargs)
        try:
            tmpl = (env.get_template if is_file else env.from_string)(template)
            return tmpl.render(**context)
        except jinja2.exceptions.TemplateNotFound as exc:
            raise TemplateNotFound(str(exc))