See #3315 and <http://docutils.sourceforge.net/docs/ref/rst/restructuredtext.html#simple-tables>.

```
% pandoc -f org -t html5
+-----------+-------+----------+
| First     | 12.0  | Example  |
|           |       | row      |
|           |       | spanning |
|           |       | lines    |
+-----------+-------+----------+
| Second    | 5.0   | Another  |
+-----------+-------+----------+
^D
<table style="width:43%;">
<colgroup>
<col style="width: 16%" />
<col style="width: 11%" />
<col style="width: 15%" />
</colgroup>
<tbody>
<tr class="odd">
<td>First</td>
<td>12.0</td>
<td>Example row spanning lines</td>
</tr>
<tr class="even">
<td>Second</td>
<td>5.0</td>
<td>Another</td>
</tr>
</tbody>
</table>
```

