Don't strip <thead>, <tbody> & <tfoot> tags in tables

[EvitanRelta]

The coloring for the rows might be different if they are stripped:

Description	HTML-in-markdown	Rendered HTML
No <thead>, <tbody> nor <tfoot>	<table> <tr> <th>Header 1</th> <th>Header 2</th> </tr> <tr> <td>Cell 1.1</td> <td>Cell 1.2</td> </tr> <tr> <td>Cell 2.1</td> <td>Cell 2.2</td> </tr> </table>	Header 1 Header 2 Cell 1.1 Cell 1.2 Cell 2.1 Cell 2.2
With <thead> and <tbody> only	<table> <thead> <tr> <th>Header 1</th> <th>Header 2</th> </tr> </thead> <tbody> <tr> <td>Cell 1.1</td> <td>Cell 1.2</td> </tr> <tr> <td>Cell 2.1</td> <td>Cell 2.2</td> </tr> </tbody> </table>	Header 1 Header 2 Cell 1.1 Cell 1.2 Cell 2.1 Cell 2.2
With <thead>, <tbody> and <tfoot>	<table> <thead> <tr> <th>Header 1</th> <th>Header 2</th> </tr> </thead> <tbody> <tr> <td>Cell 1.1</td> <td>Cell 1.2</td> </tr> </tbody> <tfoot> <tr> <td>Cell 2.1</td> <td>Cell 2.2</td> </tr> </tfoot> </table>	Header 1 Header 2 Cell 1.1 Cell 1.2 Cell 2.1 Cell 2.2