I've been thinking for a while that it's about time I did that. Those
images used to link to the Java versions of the puzzles, back when
Java was the in-browser applet platform of choice; then I made them
not link to either one when it wasn't clear which system would win;
but now JS has clearly won, it's past time the images linked to the JS
puzzles, as the obviously sensible default.

Not sure how I managed to write the former by mistake, but I didn't
notice because browsers didn't immediately complain. Still, James
Harvey points out, it ought to be turned into the actually
standards-compliant spelling of the tag. Ahem.

It's a pain having to commit each of these separately in order to test
the script, but there we go. Should be working now.

I missed some spaces in the autogenerated <span>s, and I generated the
web page components including unfinished puzzles by mistake.

This should simplify the process of adding a new puzzle, by automating
the part where I have to manually edit index.html separately from the
main build step.