Missing Comments in HTML writer

[criztovyl]

This is:

- [ ] a bug report
- [x] a feature request
- [x] **not** a usage question (ask them on https://stackoverflow.com/questions/tagged/phpspreadsheet or https://gitter.im/PHPOffice/PhpSpreadsheet)

What is the expected behavior?

Cell comments are included in the HTML produced by the HTML writer.

What is the current behavior?

Comments are not included.

What are the steps to reproduce?

<?php

require __DIR__ . '/vendor/autoload.php';

// Create new Spreadsheet object
$spreadsheet = new \PhpOffice\PhpSpreadsheet\Spreadsheet();

$spreadsheet->getActiveSheet()->getCell("A1")->setValue("Without Comment");
$spreadsheet->getActiveSheet()->getCell("A2")->setValue("With Comment");

$spreadsheet->getActiveSheet()->getComment("A2")
    ->getText()->createTextRun("This is a comment.");

$writer = \PhpOffice\PhpSpreadsheet\IOFactory::createWriter($spreadsheet, "Html");
$writer->save("comments.html");

// Comments are missing

Which versions of PhpSpreadsheet and PHP are affected?

All (feature request)