Improve Security

[thatfiredev]

The library currently works fine if all the documents are searchable by all users. But some use cases might require securely limiting results.
For example, we can't let user A find notes that were created by user B. User A should only be able to read notes created by them.
We need to find a way to handle that use case.

[thatfiredev]

Maybe we could use Callable Functions for this. I'll give it a try once I'm done with #8