Derived Stores

[crutchcorn]

This PR implements an initial Derived class implementation:

const count = new Store(10);

const doubleCount = new Derived([count], () => {
  return count.state * 2;
})

doubleCount.subscribe(() => console.log(doubleCount.state));
count.setState(() => 20);

This Derived implementation even solves the diamond problem:

Where writes to "a" will call "d" twice (with a flicker of incorrect data known as a "Glitch") because of the dual-derived nature. Our implementation does not have this problem and therefore can be considered "glitch-free"

This is a push-based/hot signals implementation

Benchmarks

Due to the relatively naive nature of this code (I wrote it in one night at ~midnight) there are performance implication in using this. Namely, in our benchmarks we are a far cry from Angular or Solid's implementation, but come close to Vue's implementation: