* Fix visit docs for Racket & support racket-xp
- Fix Racket's +lookup/documentation in the same way as
https://github.com/hlissner/doom-emacs/commit/f20f477a44138d3bc8b
- Support the +xp feature which enables racket-xp. When it's not
enabled, default handlers to the traditional racket-repl
(which requires users to run code first)
* PR feedback
* Replace add-hook! with add-hook