fix(emacs/lean-mmm-lua): add 'insert' for mmm-insert-region (C-c % l)

Related issue: #74, https://github.com/flycheck/flycheck/issues/349, https://github.com/purcell/mmm-mode/issues/32

src/emacs/lean-mmm-lua.el

@@ -9,7 +9,7 @@
   (require 'mmm-mode)
   (require 'mmm-auto)
   (require 'lua-mode)
-  (setq mmm-global-mode 'buffers-with-submode-classes)
+  (setq mmm-global-mode 'maybe)
   (setq mmm-submode-decoration-level 0)
   (eval-after-load 'mmm-vars
     '(progn
@@ -18,6 +18,7 @@
         '((lua-inline
            :submode lua-mode
            :face mmm-code-submode-face
+           :insert ((?l lean-tag nil @ "(*\n" @ " " _ "" @ "\n*)" @))
            :front "[(][*]"
            :back "[*][)]")))
        (mmm-add-mode-ext-class 'lean-mode "\\.lean" 'lean-lua))))