Add support for while and case

[Applelo]

When I use case or while loop, I get an error in my code because your plugin doesn't support it.

You can reproduce the bug with the code of the pug documentation

- var n = 0;
ul
  while n < 4
    li= n++

- var friends = 1
case friends
  when 0: p you have no friends
  when 1: p you have a friend
  default: p you have #{friends} friends