add ability to create a new backend

[ghost]

Using the examples it's unclear how to create a new backend.

[imjoey]

hi, in the latest version 0.3.6, you could create a new backend with the following codes.

        # Firlst, parse the file to create config.Configuration instance
        self.parser = parse.Parser(filestring=filestring)
        self.configuration = self.parser.build_configuration()

        # Second, create a new config.Backend instance
        new_be = config.Backend('new_backend', [])
        #  you could add option/config/server/user lines, which are the compositions of config-block
        new_be.add_option(config.Option('timeout', ''))
        # Finally, append the newly created
        self.configration.backends.append(new_be)

        // Now the `self.configuration` object contains the new backend instance
        self.render = render.Render(self.configration)
        self.render.dumps_to('./hatest.cfg')

Maybe the usage is unidiomatic. I should have set an empty list as the default value of config_block parameter when creating the config.Backend instance. What do you think? please let me know.

[ghost]

Thanks!