Add external sources feature.

[rguarascia]

This gives the ability to load from external JSON's or directly from the Github main JSON itself. This enables users to get the latest index.json, without having to update the package just to get a new list of domains. Furthermore this enables users to load from an external source, such as a CDN within their organization.

I have updated the test to reflect the new options field, and have also added a customer error class to enable clean catches.

[deepsource-io]

Here's the code health analysis summary for commits c057ab2..ae592bb. View details on DeepSource ↗.

Analysis Summary

Analyzer	Status	Summary	Link
JavaScript	❌ Failure	❗ 9 occurences introduced 🎯 1 occurence resolved	View Check ↗

---

💡 If you’re a repository administrator, you can configure the quality gates from the settings.

[IntegerAlex]

Thank you for your contribution, It adds great flexibility with external source support while maintaining backward compatibility. If it doesn't break code for others i am happy.