Make API location configurable

[corani]

At the moment the API endpoint is hardcoded to readwise.io/api/v2 (Specifically: https://readwise.io/api/v2/books/ and https://readwise.io/api/v2/highlights/). Would it be possible to make this configurable, so instead of using the official API you could use an alternative API?

I had a look at the API documentation and it seems super simple to build your own clone for just the highlights, something which I'm planning to do to setup an automatic sync from my notes/highlights in Moon+ Reader (which already supports setting a custom endpoint).