Allow placing HTML comments near table cells

Adding the comment like below prevents the rendering of tables.

| Heading |  <!-- comment -->
| ------- |
| Content |

It is in odds with the behavior of quotes and codeblocks.

> HTML comments are useful  <!-- comment -->
> -- Tejasvi

HTML comments are useful
– Tejasvi

```python <!-- comment -->
def f(): print("Hello")
def f(): print("Hello")

The struggle toward a unified markdown syntax definition (in the midst of the Babel of all the different flavors and implementations) has ultimately led toward a commonly agreed upon spec, CommonMark:

GitHub also adheres to this spec, for both markdown and GFM (GitHub Flavored Markdown):

Any suggestions to alter the markdown syntax or the expected behavior of its parsers, should really go through proposals and discussions at the CommonMark project — otherwise GFM would be departing from the spec.