[Feature request] Support for rowspan

[kuba-orlik]

Given a table using rowspans like this:

<table-saw breakpoint="(max-width: 600px)">
  <table>
    <thead>
      <tr>
	<th>Type</th>
	<th>Name</th>
      </tr>
    </thead>
    <tbody>
      <tr>
	<td rowspan="2">Fruits</td>
	<td>apple</td>
      </tr>
      <tr>
	<td>banana</td>
      </tr>
      <tr>
	<td rowspan="2">Vegetables</td>
	<td>carrot</td>
      </tr>
      <tr>
	<td>onion</td>
      </tr>
    </tbody>
  </table>
</table-saw>

The mobile view is messing up the rows:

In this example each group would have two rows and the labels should match the values: