Link colouring for `<a>` tags with subelements

[trevorcampbell]

If you check out https://github.com/joelostblom/viz-oer/tree/407c3267ae5f2a854d029626a2b19fc8d869e4f2 , you'll see that links to changed pages are not coloured properly.

I think it might be because the <a> tag has a sub <span> tag that overwrites style for the text inside. One possible solution: when colouring links, traverse to the lowest content element and wrap it in a <span> or <div> or something that adds a particular class. Even better would be to prevent subelements from overriding the <a>'s style (to avoid adding extra elements), but I'm not sure that's possible...

[joelostblom]

Note that after I switched to use the branch from #18, it seems like links are now colored correctly, although the overall formatting is a bit odd. For an example, see https://joelostblom.github.io/viz-oer/diff29/index.html:

This PR joelostblom/viz-oer#29