Add pathological test for commonmark/cmark#178.

commonmark/commonmark.js@903f35e
Author: John MacFarlane <jgm@berkeley.edu>
Date:   Fri Aug 30 16:24:48 2019 -0700

Fix pathological case commonmark/cmark#178.

commonmark/commonmark.js@34b8f65
Author: John MacFarlane <jgm@berkeley.edu>
Date:   Fri Aug 30 16:28:09 2019 -0700

test/cmark-test.el

@@ -361,6 +361,18 @@ Otherwise, MESSAGE is appended to the ERROR-BUFFER."
            cases)
           (setq x (* 10 x))))
 
+      (let ((x 1000))
+        (while (<= x 10000)
+          (push
+           (make-cmark--pathologicalTest
+            :name (concat
+                   (number-to-string x)
+                   " openers and closers multiple of 3")
+            :input (concat "a**b" (cmark--repeat "c* " x))
+            :expected (concat "<p>a**b" (cmark--repeat "c* " (1- x)) "c*</p>\n"))
+           cases)
+          (setq x (* 10 x))))
+
       (let ((x 1000))
         (while (<= x 10000)
           (push