Rewrite answers.py to match the TS version

[gvanrossum-ms]

I have a feeling we need to improve the answer generation, and my best bet is that we would be better off copying the logic of the TypeScript answer generation code.

This is a pretty big project (you almost have to start from scratch) but it is self-contained -- almost all the current logic is in answers.py.

[gvanrossum]

Did this in #173 but the results are disappointing: fewer correct answers on the (internal) standard benchmark.