racket-xp-mode is an optional minor mode that enhances the racket-mode to
explain and explore Racket code. The racket-xp-mode is started with a mode-hook
on racket-mode. Deprecated racket-mode functions are replaced with their
racket-xp-mode versions. The remaining racket-xp-mode functions are added to
keybindings as per Spacemacs conventions.
Also add the racket-mode directory to .gitignore.
