Major rewrite of doom module API

+ Fix #446, where the .local/packages.el cache was generated with
  a faulty load-path.
+ Entries in the doom-modules hash table are now plists, containing
  :flags and :path, at least.
+ Add doom-initialize-modules for loading module config.el files.
+ Add doom-module-get for accessing this plist, e.g.

    (doom-module-get :some module)         ; returns plist
    (doom-module-get :some module :flags)  ; return specific property

+ Replace doom-module-enable with doom-module-set, e.g.

    (doom-module-set :some module :flags '(+a +b +c))

+ Remove doom-module-flags (use doom-module-get instead)
+ Rename doom-module-enabled-p with doom-module-p
+ Replace doom-module-path with doom-module-find-path and
  doom-module-expand-file. The former will search for an existing module
  or file in doom-modules-dirs. The latter will expand the path from
  whatever path is stored in doom-modules.
+ Replace doom-module-paths with doom-module-load-path
+ Changed doom! to allow for nested doom! calls by delaying the loading
  of module config.el files until as late as possible.
+ Refactor doom-initialize-packages to only ihitialize package state
  (i.e. doom-packages, package-alist, and quelpa-cache), rather than its
  previous behavior of loading all Doom files (and sometimes all module
  files). This is faster and more predictable.

core/autoload/packages.el

@@ -3,10 +3,9 @@
 (load! cache)
 (require 'use-package)
 (require 'quelpa)
+(require 'package)
 (require 'async)
 
-(doom-initialize-packages)
-
 ;;;###autoload
 (defun doom-refresh-packages (&optional force-p)
   "Refresh ELPA packages."
@@ -113,7 +112,7 @@ Warning: this function is expensive; it re-evaluates all of doom's config files.
 Be careful not to use it in a loop.
 
 If INSTALLED-ONLY-P, only return packages that are installed."
-  (doom-initialize-packages t)
+  (doom-initialize-packages 'internal)
   (cl-loop with packages = (append doom-core-packages (mapcar #'car doom-packages))
            for sym in (cl-delete-duplicates packages)
            if (and (or (not installed-only-p)
@@ -146,7 +145,7 @@ containing (PACKAGE-SYMBOL OLD-VERSION-LIST NEW-VERSION-LIST).
 If INCLUDE-FROZEN-P is non-nil, check frozen packages as well.
 
 Used by `doom//packages-update'."
-  (doom-initialize-packages t)
+  (doom-initialize-packages 'internal)
   (require 'async)
   (let (quelpa-pkgs elpa-pkgs)
     ;; Separate quelpa from elpa packages
@@ -184,7 +183,7 @@ Used by `doom//packages-update'."
 depended on.
 
 Used by `doom//packages-autoremove'."
-  (doom-initialize-packages t)
+  (doom-initialize-packages 'internal)
   (let ((package-selected-packages
          (append (mapcar #'car doom-packages) doom-core-packages)))
     (append (package--removable-packages)
@@ -204,7 +203,7 @@ If INCLUDE-IGNORED-P is non-nil, includes missing packages that are ignored,
 i.e. they have an :ignore property.
 
 Used by `doom//packages-install'."
-  (doom-initialize-packages t)
+  (doom-initialize-packages 'internal)
   (cl-loop for desc in (doom-get-packages)
            for (name . plist) = desc
            if (and (or include-ignored-p