Implement combineLatest for AsyncIterable

[mattpodwysocki]

IxJS version:

Code to reproduce:

Expected behavior:

Actual behavior:

Additional information:

Add combineLatest which mirrors zip but will track the latest from each AsyncIterable input.

function delay(time) {
  return new Promise(res => setTimeout(res, time));
}

async function* delayEvery(value, time) {
  while (1) {
    await delay(time);
    yield value;
  }
}

const s1 = delayEvery(42, 500);
const s2 = delayEvery(56, 1250);

const s3 = combineLatest(s1, s2);
for await (const [fst, snd] of s3) {
  console.log(`{fst} - {snd}`);
}

[mattpodwysocki]

Closed by #132