title: How to reuse NerdTree core function with API?
body: <p>I'm looking for a way to reuse core nerdtree functions on NERDTreeAddKeyMap callback function but i did not find a way to do it after looking up on net.</p>
  
  <p>I tried a few things like the one bellow :</p>
  
  <pre><code>call NERDTreeAddKeyMap({                                                         
    \ 'key': '&lt;Left&gt;',                                                             
    \ 'scope': 'Node',                                                             
    \ 'callback': 'NerdTest' })                                                    
  
  function! NerdTest(node)                                                         
    call closeCurrentDir(a:node)                                                                                                                                                                           
  endfunction
  </code></pre>
  
  <p>But i hit this error when trying to press  on a directory</p>
  
  <pre><code>E117: Unknown function: closeCurrentDir
  </code></pre>
  
  <p>Any suggestions ?</p>
  
  <p>Best regards,</p>