Improve performance

[sindresorhus]

By using a queue data structure.

Closes #46

[neverendingqs]

LGTM. FYI, running the same perf scenario in #46 results in a runtime of ~340 ms.

const limit = plimit(10000000);
const start = Date.now();
await Promise.all([...Array(100000)].map(_ => limit(async () => Promise.resolve())));
console.log(Date.now() - start, 'plimit');

[sindresorhus]

The extra 40ms is probably because I'm using classes and yallist uses plain functions. Doesn't matter though. V8 will eventually make it as fast or faster.

[sindresorhus]

Thanks for bringing this up and testing 🙌🏻