Auto-click-auto

Added

- The fish configuration file for custom completions, ~/.config/fish/completions/{program_name}.fish
(notice it's specific to the program name), is created if it doesn't already exist. ~/.bashrc and
~/.zshrc configuration files, which are used to set up shell completion, are generic and we can assume
the users have already created them.

Fixed

- Handle exception when `auto-click-auto` cannot infer the shell type from the `SHELL` environment variable

Added

- Package typing information

Changed

- Function `enable_click_shell_completion` now has the `shells` positional argument set by default to `None`

Added

- Function `enable_click_shell_completion` to automatically add autocomplete support
for the Bash, Zsh, and Fish shells
- Decorator `enable_click_shell_completion_option` to easily add an option to Click commands for autocomplete
support