Add support for grid tables

[digitalmoksha]

One request/complaint I've heard from folks using markdown is the inability to have block content in cells, particularly lists and multiple paragraphs.

It's possible to do this by mixing an HTML table with markdown, such as

<table>
<tr>
<td>

- built-in wrapper
- bright color

</td>
</tr>
</table>

However many would like to use a markdown syntax rather than directly coding HTML tables. It makes reading the markdown source much more usable.

"Grid tables", as opposed to "pipe tables" available in the GFM spec, allow for a table to be built using markdown and include content blocks in the cells, as well as supporting irregular cells/rows.

An example

+---------------+---------------+--------------------+
| Fruit         | Price         | Advantages         |
+===============+===============+====================+
| Bananas       | $1.34         | - built-in wrapper |
|               |               | - bright color     |
+---------------+---------------+--------------------+
| Oranges       | $2.10         | - cures scurvy     |
|               |               | - tasty            |
+---------------+---------------+--------------------+

Both pandoc and markdig support such a syntax. (I don't know yet if there are any differences between their syntaxes).