More built-in shell configurations

[k9withabone]

This is a tracking issue for adding more built-in shell configurations. For a shell to work with autocast, it must accept input on its stdin. The prompt should be changed to something unique so that autocast does not mistake something in a command's output as the prompt. See the bash defaults for an example. If you get a custom shell working, please comment with your configuration and I'll add it to autocast. Feel free to suggest other shells you would like to see built-in configurations for to be added to the list.

• zsh
• fish
• nu