feature/lookup: rewrite dash docset integration

+ Uses alist variable to store config, rather than hooks
+ Added check for installed docsets in +lookup/documentation
+ Set docsets for various language modules (c-mode, c++-mode, css-mode,
  scss-mode, sass-mode, web-mode, go-mode, racket-mode, emacs-lisp-mode,
  js2-mode, rjsx-mode, typescript-mode, rust-mode, and php-mode)
+ Made *eww* popups for dash docsets larger
+ Renamed set-docset! => set-docsets! (set-docset! is aliased to
  set-docsets!)
+ New +lookup/install-docset alias

modules/lang/racket/config.el

@@ -8,7 +8,7 @@
   (set-lookup-handlers! 'racket-mode
     :definition    #'racket-visit-definition
     :documentation #'racket-describe)
-  (set-docset! 'racket-mode "Racket")
+  (set-docsets! 'racket-mode "Racket")
   (set-pretty-symbols! 'racket-mode
     :lambda  "lambda"
     :map     "map"