Use a more conventional testing framework

[gobengo]

npm test right now uses some simple functions I built myself (in test/index.ts). They're fine, but not conventional. And can be confusing, not to mention limiting when trying to figure out which test is failing.

We should replace it with something like node-tape, mocha, or jest. Probably jest. I haven't used it at scale but seems to be growing in popularity and I think can do nice parallelization.

[gobengo]

I have had good experience with. https://github.com/alsatian-test/alsatian