This PR:

• Creates the optional onResponse option that is a callback function that allows the developer to modify the contents of the parsed response body, in the event there needs to be custom logic or sources for different properties. For example, say the targeted website does not provide opengraph description, the developer might want to instead have the description be the text contents of the first p tag. Additionally, an instance of the URL object has been exposed so the callback could contain site-by-site considerations.
• Creates a test for onResponse functionality.
• Updates README to provide documentation and use case for onResponse
• Defines Type ILinkPreviewResponse for the actual library response for type safety.

Tests passed locally (Github CI tests might break due to bot detection)

This PR will resolve #159