feat!: Migrate to `fetch`

As we plan to support multiple environments and runtimes it makes sense to migrate from `node-fetch` to the [Fetch API](https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API). Transitioning this library to a interface on top of `fetch` provides a ton of flexibility and will greatly decrease package size.

Additionally:

- [ ] Update Github "about" section to:
```
An HTTP request client that provides a lightweight interface on top of `fetch`.
```