title: Vim folding - mark opened folds
body: <p>Is there a way to see, where are opened folds in current File? 
  I personally have the problem when opening folds and moving around, I'm not able to find the line where the fold was started from! Maybe there is an option to set a nice-looking folding-hint next to the numbers. Maybe like this:</p>
  
  <pre><code>+ 1 void myfunc(void) {
  | 2     printf("Hello World\n");
  | 3     printf("Goodby World!\n");
  - 4 }
    5
    6 void anotherfunc(void)
  ...
  </code></pre>
  
  <p>it would be very nice! I already used google and also used the vim-help but found no way to do this.</p>
  
  <p>Kind regards,
  musicmatze</p>