Add support for standard readline (emacs) keyboard shortcuts

[dkarter]

Thank you for making this great software!

It would be good to have support for more standard keyboard shortcuts that match how most linux/macOS operating systems work.

For example:
ctrl-n: navigate down a list
ctrl-p: navigate up a list

In macOS at least, every list can be navigated this way. I use it in Neovim also to navigate completions, and in my browser to navigate the url bar and suggestions.

There is already support for ctrl-w (delete word), alt-f, alt-b in the url input, which is great. But it really messes with my muscle memory to not have ctrl-n and ctrl-p.

I know it creates a conflict with the default keybindings chosen for New and Commands, but having ctrl-n and ctrl-p reserved for navigating lists and completions will make this more intuitive.

Alternatively, it might be possible to have these keybindings be context aware - so if a context menu or command palette is open, then they can be used to navigate those, otherwise, they can be used for their current mapping.

For reference: https://readline.kablamo.org/emacs.html