Relative links in exercise explanations are incorrect after delivery

[maxg]

deliver-handouts translates relative links on delivery to remove the handout directory level, but exercise explanations have already been removed, so links in those explanations end up broken unless they use the web-ready form.

One fix would be to include the (possible) exercise JSON file in the set of files to translate.

[maxg]

Still a problem using Lambda delivery because when fixRelative is called on the metadata, quotation marks are escaped and the regular expressions do not match.

[rcmiller]

worked around with a link that contains both urls, e.g.:

<a class="no-markdown" href="../../general/#who-to-ask" data-local-href="../../../general/handout/index.html#who-to-ask">ask for help</a>

with code in handout-run.js that replaces href with data-local-href when viewed locally.