New approach for checking we are loading the right file

[t8y8]

This subsumes #60.

Here's an approach for feedback, I pulled the logic up into the xml_open class because otherwise I'd need to pass the root tag all the way down through the helper functions and it made the try-with-if-raise nesting complex in find_file_in_zip.

I want to clean up a bit more of that logic, but this is a good start for feedback

[graysonarts]

🚀