org.el (org-provide-todo-statistics): Allow to set to a list of two lists, for TODO and DONE keywords

* org.el (org-provide-todo-statistics): Allow to set to a list
of two lists, one with TODO keywords, the other one with DONE
keywords.
(org-update-parent-todo-statistics): Correctly handle
`org-provide-todo-statistics' when it is set as a list of two
lists, for TODO and DONE keywords.

Thanks to Fletcher Charest for reporting this and requesting
this feature.

lisp/org.el

@@ -2567,6 +2567,9 @@ ALL-HEADLINES means update todo statistics by including headlines
 with no TODO keyword as well, counting them as not done.
 A list of TODO keywords means the same, but skip keywords that are
 not in this list.
+When set to a list of two lists, the first list contains keywords
+to consider as TODO keywords, the second list contains keywords
+to consider as DONE keywords.
 
 When this is set, todo statistics is updated in the parent of the
 current entry each time a todo state is changed."
@@ -2576,6 +2579,9 @@ current entry each time a todo state is changed."
 	  (const :tag "Yes, including all entries" all-headlines)
 	  (repeat :tag "Yes, for TODOs in this list"
 		  (string :tag "TODO keyword"))
+	  (list :tag "Yes, for TODOs and DONEs in these lists"
+		(repeat (string :tag "TODO keyword"))
+		(repeat (string :tag "DONE keyword")))
 	  (other :tag "No TODO statistics" nil)))
 
 (defcustom org-hierarchical-todo-statistics t
@@ -12710,13 +12716,25 @@ statistics everywhere."
 	    		       (match-string 2)))
 	    	(if (or (eq org-provide-todo-statistics 'all-headlines)
 	    		(and (listp org-provide-todo-statistics)
+			     (stringp (car org-provide-todo-statistics))
 	    		     (or (member kwd org-provide-todo-statistics)
-	    			 (member kwd org-done-keywords))))
+	    			 (member kwd org-done-keywords)))
+			(and (listp org-provide-todo-statistics)
+			     (listp (car org-provide-todo-statistics))
+			     (or (member kwd (car org-provide-todo-statistics))
+				 (and (member kwd org-done-keywords)
+				      (member kwd (cadr org-provide-todo-statistics))))))
 	    	    (setq cnt-all (1+ cnt-all))
 	    	  (if (eq org-provide-todo-statistics t)
 	    	      (and kwd (setq cnt-all (1+ cnt-all)))))
-	    	(and (member kwd org-done-keywords)
-	    	     (setq cnt-done (1+ cnt-done)))
+	    	(when (or (and (listp org-provide-todo-statistics)
+			       (listp (car org-provide-todo-statistics))
+			       (member kwd org-done-keywords)
+			       (member kwd (cadr org-provide-todo-statistics)))
+			  (and (listp org-provide-todo-statistics)
+			       (stringp (car org-provide-todo-statistics))
+			       (member kwd org-done-keywords)))
+		  (setq cnt-done (1+ cnt-done)))
 	    	(outline-next-heading)))
 	    (setq new
 	    	  (if is-percent