Programmable Property-Based Testing

Example:

   const point = arb.from((pick) => {
      const x = pick(arb.int(0, 100));
      const y = pick(arb.int(0, 100));
      return { x, y };
   });

It also lets you parse objects instead of generating them if you define a Domain instead of an Arbitrary, which I haven't actually needed much, but seems neat.

It does some shrinking without having to implement anything extra, but I haven't done anything with code coverage-guided generation. I'd like to try that sometime.