Commit 3 -- Input and key-derivation now actually works

I've worked out the bugs with the input and key term derivation (since I
coded the original thing after waking up from a dream at like 2 am), and
now all that's left for this part is to actually create the script.

There's a basic test file located in the earlier commits, but it's just
chaff. The real testing will come as the script gets developed.

Commentary is helpful!