Add oldestArchive option to isArchived method

[sekedus]

Issue: #7

Description of changes:

• Add oldestArchive option to isArchived method
• Update README.md with detailed usage and API docs

The isArchived method now accepts an options object, allowing users to request the oldest available archive with the oldestArchive flag.

README.md and wayback.test.js have been updated to reflect this new functionality.

---

Example:

import { Wayback } from './src/wayback.js';

const wayback = new Wayback({
    connectionTimeoutMs: 300000  // 5 minutes in milliseconds
});
const result = await wayback.isArchived('http://microsoft.com', { oldestArchive: true });
console.log(result);