att: save the outer terminal's environment

Signed-off-by: Christopher Larson <kergoth@gmail.com>
att-env: add script to show the outer terminal env

Signed-off-by: Christopher Larson <kergoth@gmail.com>
fish: add att-update-env function, ala tmux-update-env

Signed-off-by: Christopher Larson <kergoth@gmail.com>