- Move Doom core elisp API demos out of docs/examples.org into lisp/demos.org.
- Recognize and search demos.org file in modules for additional
demos (including $DOOMDIR/demos.org).
- Refactor emacs-lisp module to use new elisp-demos-user-files variable
instead of an advice. This way, elisp-demo's commands (such as
`elisp-demos-find-demo` and `elisp-demos-add-demo`) will include
Doom's demos.
