With Markdown tables, one can control column alignment:

```markdown
| left | center | right |
| :--- | :----: | ----: |
| a    | b      | c     |
```

To enable this non-standard (in docutils) feature, MyST-Parser adds CSS classes to the `td`/`th`,
which then require implementation by the HTML themes.

This will catch basic issues in PRs.

This enables providing custom URLs for alternative VCS hosts.

This now uses the current `basic-ng` template for determining when
and how to present the edit button.