Add and expand doom/help* commands

Adds the following commands:

- doom/help (opens the Doom manual)
- doom/help-search (for searching through org headlines in Doom's
  documentation)
- doom/help-faq (for searching the FAQ)
- doom/help-news (for browsing the Doom newsletters)
- doom/help-autodefs (renamed from doom/describe-autodef -- for looking
  up documentation on autodef function/macros, like
  `set-lookup-handler!`)
- doom/help-modules (renamed from doom/describe-module, for jumping to a
  Doom module's documentation)
- doom/help-packages (renamed from doom/describe-package and recently
  fixed -- looks up information about installed packages, including what
  Doom module(s) install it and where it is configured)
- doom/help-package-config (for searching and jumping to any block where
  a package is configured in Doom Emacs)

Also adds the SPC h d (or C-h d) prefix for Doom-specific help commands.
SPC h D will invoke doom/help.

However, the documentation itself hasn't been committed yet, so some of
these commands may be useless atm. Sorry!

core/autoload/packages.el

@@ -219,9 +219,9 @@ files."
                   (push (cons name
                               (plist-put plist :modules
                                          (cond ((file-in-directory-p file doom-private-dir)
-                                                (list :private))
+                                                '((:private)))
                                                ((file-in-directory-p file doom-core-dir)
-                                                (list :core))
+                                                '((:core)))
                                                ((doom-module-from-path file)))))
                         doom-packages))))))
       ((debug error)