pandoc-template-mode.el: Improve.

Avoid highlighting of "strings" by deriving from
`text-mode-syntax-table`. This fixes missing highlighting in default.html5
tag attributes.

Define comment starting and ending sequences to allow use of M-q (auto-fill)
on comments.

tools/pandoc-template-mode.el

@@ -52,9 +52,13 @@
  ;;;###autoload
 (define-derived-mode pandoc-template-mode fundamental-mode "Pandoc-Template"
   "A major mode for editing Pandoc-Template files."
-  :syntax-table nil
+  :syntax-table text-mode-syntax-table
   (setq-local font-lock-defaults
-              '(pandoc-template-font-lock-keywords)))
+              '(pandoc-template-font-lock-keywords))
+  (setq-local comment-start "$--")
+  (setq-local comment-start-skip "\\$--[ \t]*")
+  (setq-local comment-end "")
+  (setq-local comment-end-skip "[ \t]*$"))
 
 (provide 'pandoc-template-mode)
  ;;; pandoc-template.el ends here