Fetch convenience wrapper

[peterboyer]

Similar idea to #2, however because fetch is so commonly poly-filled etc, perhaps this should offer a factory function that accepts fetch as well as a default that attempts to use window.fetch (as offered by the global environment).

// default exported `fetch` as from `Fetch(fetch)`.
import { fetch } from `@armix/terror/fetch`;
const $response = await fetch("/api/...", { options });

// create from your own polyfill and wrap with `Fetch(...)`
import { Fetch } from `@armix/terror/fetch`;
import { fetch as _fetch } from "fetch-polyfill";
export const fetch = Fetch(_fetch);
const $response = await fetch(...);