`unwrap` and `expect` in the code

[NightBlaze]

There are some unwrap and expect calls not only in tests but also in real code. It prevents from using the lib in apps with high crash-free standards.

[James-LG]

Yes the readme does say

This library is major-version 0 because there are still todo! calls for many xpath features. If you encounter one that you feel should be prioritized, open an issue on GitHub.

But I am curious which panics you ran into, maybe I can deal with them sooner rather than later.