Infer pipe table column widths from separator row

[Amberg]

Hi

First off, thank you for your great library — I use it to convert Markdown to Open XML in my DocxTemplater, and it’s been working beautifully.

In my use case, I needed a way to control column widths in pipe tables. Unfortunately, the grid table syntax wasn't an option because it requires monospaced fonts.

This PR introduces a small but useful enhancement:

What’s included

• Adds support for inferring column widths in pipe tables based on the number of dashes in the header separator row.
• Activates this behavior via a new option: PipeTableOptions.InferColumnWidthsFromSeparator.
• Includes unit tests to ensure the feature works with different table layouts and dash distributions.

This allows authors to write tables like:

A | B | C
--|----|--

…to get column widths of 25%, 50%, 25%, depending on the relative dash count.

Let me know if you'd like changes or further refinements — happy to adjust!

Thanks again for your work!