title: what is autoTableHtmlToJson and where is converting html page?
body: <p>What is <code>autoTableHtmlToJson</code>? I do not understand. Also how occurs 'columns' and 'data' ?
  Where is html page?</p>
  
  <pre><code>var res = doc.autoTableHtmlToJson(this.dataGrid.table.nativeElement);
  doc.autoTable(res.columns, res.data, {
      startY: 20,
      columnStyles: { text: { columnWidth: 'auto' } }
  });
  </code></pre>