refactor: simplify authorization API

[wescopeland]

Resolves #105.

All functions can now be called without needing to build an authorization object, eg:

import { getGame } from "@retroachievements/api";

const webApiKey = "<your web API key>";

// This returns basic metadata about the game on this page:
// https://retroachievements.org/game/14402
const game = await getGame(webApiKey, { gameId: 14402 });