make_link_table: include parent nodes

[zkamvar]

I've been bashing my head against this wall for the last half hour and finally figured out what's going on.

In the lesson transition, I use the $node column of the table to fix any broken links without having to re-read the document. This works for markdown images, but for HTML images, this does not work even though they are present in the table because they are parsed from the text and only exist as ephemeral nodes that the original document does not know about. This leads to patterns where I attempt to fix these in-place, but eventually fail and have to fix them manually.

Having the parent node will allow me to detect the underlying HTML node and fix the images that way.