Fix: use Menu 'menu' prop, not 'name'; support w-sp in menu props

- 'name' is a separate 'identifier'-like Menu property. So use ":menu"
to get the menu entry 'name' (not to be confused with the menu 'name'
property!)
- Allow white space in menu entry 'name' (Example:
https://discourse.gohugo.io/t/working-with-multiple-menus-and-iterating-over-the-whole-set/7503)
- Refactor: menu-name(-str) -> menu-entry(-str) to prevent confusing
that with the menu name property.
- Remove 'children' from the list of settable Menu properties. As its
datatype is "Menu" and not "string" (from docs), I don't see that as
something a user would set. I believe, a user setting a menu parent
will mirror that menu entry as a child automatically in that parent
entry.
- Allow inheritance of HUGO_FRONT_MATTER_FORMAT property too.
- Add examples of white space use in ":menu" and ":name" for TOML and
YAML front matter

example-site/content-org/all-posts.org

@@ -242,7 +242,7 @@ ORG_ADD_CONTRIB = org-eldoc ox-extra org-mime
 :PROPERTIES:
 :EXPORT_FILE_NAME: menu-alist-meta-data-toml
 :EXPORT_DATE: 2017-07-18
-:EXPORT_HUGO_MENU: :name main :weight 80 :parent posts :identifier foo1
+:EXPORT_HUGO_MENU: :menu "something here" :weight 80 :parent posts :identifier foo1
 :END:
 Testing the addition of /menu/ alist meta data to the TOML front
 matter.
@@ -265,20 +265,36 @@ Rename or set an unique identifier.
 :PROPERTIES:
 :EXPORT_FILE_NAME: menu-alist-meta-data-toml-override-full
 :EXPORT_DATE: 2017-07-18
-:EXPORT_HUGO_MENU: :name test :weight 50
+:EXPORT_HUGO_MENU: :menu test :weight 50
 :END:
 For this post, we see that no menu properties are inherited from the
 parent; only the menu properties set in his subtree are effective.
 ** Menu Meta Data in YAML Front Matter                                 :yaml:
 :PROPERTIES:
 :EXPORT_HUGO_FRONT_MATTER_FORMAT: yaml
+:END:
+*** White space in menu entry
+:PROPERTIES:
 :EXPORT_FILE_NAME: menu-meta-data-yaml2
-:EXPORT_DATE: 2017-07-18
-:EXPORT_HUGO_MENU: :name main :weight 25 :parent posts :identifier menu-yaml
+:EXPORT_DATE: 2017-07-19
+:EXPORT_HUGO_MENU: :menu "something here" :weight 25
+:END:
+Testing the addition of /menu/ meta data to the YAML front matter.
+Here the front matter format is set to YAML using the
+=HUGO_FRONT_MATTER_FORMAT= key in property drawer.
+
+Here there is white space in menu entry keyword.
+*** White space in menu name
+:PROPERTIES:
+:EXPORT_FILE_NAME: menu-meta-data-yaml3
+:EXPORT_DATE: 2017-07-19
+:EXPORT_HUGO_MENU: :menu main :weight 25 :parent posts :name "Menu in YAML"
 :END:
 Testing the addition of /menu/ meta data to the YAML front matter.
 Here the front matter format is set to YAML using the
 =HUGO_FRONT_MATTER_FORMAT= key in property drawer.
+
+Here there is white space in menu name property.
 * TODO Pre-Draft State
 :PROPERTIES:
 :EXPORT_FILE_NAME: draft-state-todo

example-site/content-org/construct-hugo-front-matter-from-menu-meta-data.org

@@ -1,6 +1,6 @@
 #+HUGO_BASE_DIR: ../
 #+HUGO_FRONT_MATTER_FORMAT: yaml
-#+HUGO_MENU: :name main :parent posts
+#+HUGO_MENU: :menu main :parent posts
 
 * Menu Meta Data in YAML Front Matter                             :menu:yaml:
 :PROPERTIES:

example-site/content/posts/menu-alist-meta-data-toml-override-partial.md

@@ -3,7 +3,7 @@ title = "Overriding few menu properties"
 date = 2017-07-18
 tags = ["menu"]
 draft = false
-[menu.main]
+[menu."something here"]
   parent = "posts"
   weight = 10
   identifier = "ov-partial"

example-site/content/posts/menu-alist-meta-data-toml.md

@@ -1,9 +1,9 @@
 +++
-title = "Menu Alist Meta Data in TOML Front Matter"
+title = "Menu Meta Data in TOML Front Matter"
 date = 2017-07-18
 tags = ["menu"]
 draft = false
-[menu.main]
+[menu."something here"]
   parent = "posts"
   weight = 80
   identifier = "foo1"

example-site/content/posts/menu-meta-data-yaml2.md

@@ -1,13 +1,13 @@
 ---
-title : "Menu Meta Data in YAML Front Matter"
-date : 2017-07-18
+title : "White space in menu entry"
+date : 2017-07-19
 tags : ["menu", "yaml"]
 draft : false
 menu :
-  main:
-    parent : "posts"
+  "something here":
     weight : 25
-    identifier : "menu-yaml"
 ---
 
 Testing the addition of *menu* meta data to the YAML front matter. Here the front matter format is set to YAML using the `HUGO_FRONT_MATTER_FORMAT` key in property drawer.
+
+Here there is white space in menu entry keyword.

example-site/content/posts/menu-meta-data-yaml3.md

@@ -0,0 +1,15 @@
+---
+title : "White space in menu name"
+date : 2017-07-19
+tags : ["menu", "yaml"]
+draft : false
+menu :
+  main:
+    parent : "posts"
+    weight : 25
+    name : "Menu in YAML"
+---
+
+Testing the addition of *menu* meta data to the YAML front matter. Here the front matter format is set to YAML using the `HUGO_FRONT_MATTER_FORMAT` key in property drawer.
+
+Here there is white space in menu name property.

ox-hugo.el

@@ -428,7 +428,7 @@ convert to an alist ((:name . \"foo\") (:weight . 80))."
   (let ((menu-alist (org-babel-parse-header-arguments menu-prop-str))
         ret)
     ;; Hugo menu properties: https://gohugo.io/content-management/menus/
-    (dolist (prop '(name url menu identifier pre post weight parent children))
+    (dolist (prop '(menu name url identifier pre post weight parent)) ;children prop is probably read-only
       (when-let* ((key (intern (concat ":" (symbol-name prop)))) ;name -> :name
                   (cell (assoc key menu-alist)))
         (push `(,prop . ,(cdr cell)) ret)))
@@ -534,24 +534,29 @@ are \"toml\" and \"yaml\"."
                      (menu-alist value)
                      ;; Menu name needs to be non-nil to insert menu
                      ;; info in front matter.
-                     (menu-name (cdr (assoc 'name menu-alist)))
-                     (menu-name-str "")
+                     (menu-entry (cdr (assoc 'menu menu-alist)))
+                     ;; Wrap the menu-entry with double quotes if it
+                     ;; contains non-alphabetical characters.
+                     (menu-entry (if (string-match-p "\\`[a-zA-Z]+\\'" menu-entry)
+                                     menu-entry
+                                   (org-hugo--wrap-string-in-quotes menu-entry)))
+                     (menu-entry-str "")
                      (menu-value-str ""))
                 (message "[menu alist DBG] = %S" menu-alist)
-                (when menu-name
-                  (setq menu-name-str (cond ((string= format "toml")
-                                             (format "[menu.%s]\n" menu-name))
-                                            ((string= format "yaml")
-                                             (prog1
-                                                 (format "menu %s\n%s%s%s\n" sign indent menu-name sign)
-                                               (setq indent (concat indent indent)))) ;Double the indent for next use
-                                            (t
-                                             "")))
+                (when menu-entry
+                  (setq menu-entry-str (cond ((string= format "toml")
+                                              (format "[menu.%s]\n" menu-entry))
+                                             ((string= format "yaml")
+                                              (prog1
+                                                  (format "menu %s\n%s%s%s\n" sign indent menu-entry sign)
+                                                (setq indent (concat indent indent)))) ;Double the indent for next use
+                                             (t
+                                              "")))
                   (dolist (menu-pair menu-alist)
                     (let ((menu-key (symbol-name (car menu-pair)))
                           (menu-value (cdr menu-pair)))
-                      ;; (message "menu DBG: %S %S %S" menu-name menu-key menu-value)
-                      (unless (string= "name" menu-key)
+                      ;; (message "menu DBG: %S %S %S" menu-entry menu-key menu-value)
+                      (unless (string= "menu" menu-key)
                         (when menu-value
                           (unless (string= menu-key "weight")
                             (setq menu-value (org-hugo--wrap-string-in-quotes menu-value)))
@@ -559,7 +564,7 @@ are \"toml\" and \"yaml\"."
                                 (concat menu-value-str
                                         (format "%s%s %s %s\n"
                                                 indent menu-key sign menu-value)))))))
-                  (setq menu-string (concat menu-name-str menu-value-str))))
+                  (setq menu-string (concat menu-entry-str menu-value-str))))
             (setq front-matter
                   (concat front-matter
                           (format "%s %s %s\n"
@@ -590,7 +595,8 @@ It does so only if `org-use-property-inheritance' is a list (or
 nil).  Otherwise it just returns the value of
 ``org-use-property-inheritance'."
   (if (listp org-use-property-inheritance)
-      (let ((prop-list '("HUGO_TAGS"
+      (let ((prop-list '("HUGO_FRONT_MATTER_FORMAT"
+                         "HUGO_TAGS"
                          "HUGO_CATEGORIES"
                          "HUGO_DRAFT"
                          "HUGO_TYPE"