RE: echo-area-keystroke-hook

[Drew Adams]

> Also see:
> 
>     https://github.com/justbur/emacs-which-key
>     https://github.com/kai2nenobu/guide-key
>       (http://pragmaticemacs.com/emacs/get-pop-up-help-for-keybindings-with-
> which-key/)

And Icicles key completion.  It is on-demand (`S-TAB'),
but you could make it automatic, on a delay if you want.

http://www.emacswiki.org/emacs/Icicles_-_Key_Completion