formatter: put topic in templatespec tuple This will allow us to change the initial template reference depending on how the template is looked up. For example, -Tdefault => (ref='changeset', tmpl=None, mapfile='map-cmdline.default') -T'{rev}' => (ref='', tmpl='{rev}', mapfile=None) A literal template given by -T option will be stored as an unnamed template, which will free up the template namespace so that we can load named templates from [templates] section of user config.