feature: the instant completion for lisp-mode.

[sakurawald]

Just like the instant completion for M-x popup window.

It would be nice to have the instant completion for lisp-mode.
For example, you can just type in

(def...

And the completion pop-up automatically without the tab key pressed.

There can also be an option to set the least characters to trigger the instant completion, like pop-up instant completion after 2 characters or 3 characters.

[sakurawald]

https://lem-project.github.io/usage/configuration/#show-the-completion-list-instantly

[sakurawald]

Another good policy is to set a automatic completoin timeout, if this value is set to 0, then it is instant completion.