Refactor to a fetch style API

[th0rgall]

The project currently relies on XMLHTTPRequest and a bad custom polyfill for XMLHTTPRequest for node.js, based on the request library.

XMLHTTPRequest is old, request is deprecated now. This causes issues that are hard to debug and that won't be solved (see Issues here). Moreover, there are better fetch alternatives available now with built-in combined browser/node support, like cross-fetch.

Any effort to restart/improve this project should start with replacing the XMLHTTPRequest dependency at its core.