title: CodeMirror custom showHint() call doesn't work
body: <p>Attempting to implement a custom <code>showHint</code> call for a spellcheck module. I've followed the <a href="https://codemirror.net/doc/manual.html#addon_show-hint" rel="nofollow noreferrer">docs</a> but calling <code>editor.showHint</code> appears to do nothing and returns <code>undefined</code>.</p>
  
  <p>I figure there is something I am missing. Here is my sandbox code to test:</p>
  
  <pre><code>editor.on('cursorActivity', function() {
      var options = {
      from: editor.getDoc().getCursor(),
      to: editor.getDoc().getCursor(),
      list: ['foo', 'bar', 'baz']
    };
    editor.showHint(options);
  });
  </code></pre>
  
  <p><a href="http://jsfiddle.net/3wvcudqt/3/" rel="nofollow noreferrer">http://jsfiddle.net/3wvcudqt/3/</a></p>